A Triangulation Checklist Born From the Question; “Why NOT Use Close Relatives for Triangulation?”

One of my readers asked why we don’t use close relatives for triangulation.

This is a great question because not using close relatives for triangulation seems counter-intuitive.

I used to ask my kids and eventually my students and customers if they wanted the quick short answer or the longer educational answer.

The short answer is “because close relatives are too close to reliably form the third leg of the triangle.” Since you share so much DNA with close relatives, someone matching you who is identical by chance can also match them for exactly the same reason.

If you trust me and you’re good with that answer, wonderful. But I hope you’ll keep reading because there’s so much to consider, not to mention a few gotchas. I’ll share my methodology, techniques, and workarounds.

We’ll also discuss absolutely wonderful ways to utilize close relatives in the genetic genealogical process – just not for triangulation.

At the end of this article, I’ve provided a working triangulation checklist for you to use when evaluating your matches.

Let’s go!

The Step-by-Step Educational Answer😊

Some people see “evidence” they believe conflicts with the concept that you should not use close relatives for triangulation. I understand that, because I’ve gone down that rathole too, so I’m providing the “educational answer” that explains exactly WHY you should not use close relatives for triangulation – and what you should do.

Of course, we need to answer the question, “Who actually are close relatives?”

I’ll explain the best ways to best utilize close relatives in genetic genealogy, and why some matches are deceptive.

You’ll need to understand the underpinnings of DNA inheritance and also of how the different vendors handle DNA matching behind the scenes.

The purpose of autosomal DNA triangulation is to confirm that a segment is passed down from a particular ancestor to you and a specific set of your matches.

Triangulation, of course, implies 3, so at least three people must all match each other on a reasonably sized portion of the same DNA segment for triangulation to occur.

Matching just one person only provides you with one path to that common ancestor. It’s possible that you match that person due to a different ancestor that you aren’t aware of, or due to chance recombination of DNA.

It’s possible that your or your match inherited part of that DNA from your maternal side and part from your paternal side, meaning that you are matching that other person’s DNA by chance.

I wrote about identical by descent (IBD), which is an accurate genealogically meaningful match, and identical by chance (IBC) which is a false match, in the article Concepts – Identical by…Descent, State, Population and Chance.

I really want you to understand why close relatives really shouldn’t be used for triangulation, and HOW close relative matches should be used, so we’re going to discuss all of the factors that affect and influence this topic – both the obvious and little-understood.

  • Legitimate Matches
  • Inheritance and Triangulation
  • Parental Cross-Matching
  • Parental Phasing
  • Automatic Phasing at FamilyTreeDNA
  • Parental Phasing Caveats
  • Pedigree Collapse
  • Endogamy
  • How Many Identical-by-Chance Matches Will I Have?
  • DNA Doesn’t Skip Generations (Seriously, It Doesn’t)
  • Your Parents Have DNA That You Don’t (And How to Use It)
  • No DNA Match Doesn’t Mean You’re Not Related
  • Imputation
  • Ancestry Issues and Workarounds
  • Testing Close Relatives is VERY Useful – Just Not for Triangulation
  • Triangulated Matches
  • Building Triangulation Evidence – Ingredients and a Recipe
  • Aunts/Uncles
  • Siblings
  • How False Positives Work and How to Avoid Them
  • Distant Cousins Are Best for Triangulation & Here’s Why
  • Where Are We? A Triangulation Checklist for You!
  • The Bottom Line

Don’t worry, these sections are logical and concise. I considered making this into multiple articles, but I really want it in one place for you. I’ve created lots of graphics with examples to help out.

Let’s start by dispelling a myth.

DNA Doesn’t Skip Generations!

Recently, someone emailed to let me know that they had “stopped listening to me” in a presentation when I said that if a match did not also match one of your parents, it was a false match. That person informed me that they had worked on their tree for three years at Ancestry and they have “proof” of DNA skipping generations.

Nope, sorry. That really doesn’t happen, but there are circumstances when a person who doesn’t understand either how DNA works, or how the vendor they are using presents DNA results could misunderstand or misinterpret the results.

You can watch my presentation, RootsTech session, DNA Triangulation: What, Why and How, for free here. I’m thrilled that this session is now being used in courses at two different universities.

DNA really doesn’t skip generations. You CANNOT inherit DNA that your parents didn’t have.

Full stop.

Your children cannot inherit DNA from you that you don’t carry. If you don’t have that DNA, your children and their descendants can’t have it either, at least not from you. They of course do inherit DNA from their other parent.

I think historically, the “skipping generations” commentary was connected to traits. For example, Susie has dimples (or whatever) and so did her maternal grandmother, but her mother did not, so Susie’s dimples were said to have “skipped a generation.” Of course, we don’t know anything about Susie’s other grandparents, if Susie’s parents share ancestors, recessive/dominant genes or even how many genetic locations are involved with the inheritance of “dimples,” but I digress.

DNA skipping generations is a fallacy.

You cannot legitimately match someone that your parent does not, at least not through that parent’s side of the tree.

But here’s the caveat. You can’t match someone one of your parents doesn’t with the rare exception of:

  • Relatively recent pedigree collapse that occurs when you have the same ancestors on both sides of your tree, meaning your parents are related, AND
  • The process of recombination just happened to split and recombine a segment of DNA in segments too small for your match to match your parents individually, but large enough when recombined to match you.

We’ll talk about that more in a minute.

However, the person working with Ancestry trees can’t make this determination because Ancestry doesn’t provide segment information. Ancestry also handles DNA differently than other vendors, which we’ll also discuss shortly.

We’ll review all of this, but let’s start at the beginning and explain how to determine if our matches are legitimate, or not.

Legitimate Matches

Legitimate matches occur when the DNA of your ancestor is passed from that ancestor to their descendants, and eventually to you and a match in an unbroken pathway.

Unbroken means that every ancestor between you and that ancestor carried and then passed on the segment of the ancestor’s DNA that you carry today. The same is true for your match who carries the same segment of DNA from your common ancestor.

False positive matches occur when the DNA of a male and female combine randomly to look like a legitimate match to someone else.

Thankfully, there are ways to tell the difference.

Inheritance and Triangulation

Remember, you inherit two copies of each of your chromosomes 1-22, one copy from your mother and one from your father. You inherit half of the DNA that each parent carries, but it’s mixed together in you so the labs can’t readily tell which nucleotide, A, C, T, or G you received from which parent. I’m showing your maternal and paternal DNA in the graphic below, stacked neatly together in a column – but in reality, it could be AC in one position and CA in the next.

For matching all that matters is the nucleotide that matches your match is present in one of those two locations. In this case, A for your mother’s side and C for your father’s side. If you’re interested, you can read more about that in the article, Hit a Genealogy Home Run Using Your Double-Sided Two-Faced Chromosomes While Avoiding Imposters.

You can see in this example that you inherited all As from your Mom and all Cs from your Dad.

  • A legitimate maternal match would match you on all As on this particular example segment.
  • A legitimate paternal match would match you on all Cs on this particular segment.
  • A false positive match will match you on some random combination of As and Cs that make it look like they match you legitimately, but they don’t.
  • A false positive match will NOT match either your mother or your father.

To be very clear, technically a false positive match DOES match your DNA – but they don’t match your DNA because you share a common ancestor with your match. They match you because random recombination on their side causes you to match each other by chance.

In other words, if part of your DNA came from your Mom’s side and part from your Dad’s but it randomly fell in the correct positional order, you’d still match someone whose DNA was from only their mother or father’s side. That’s exactly the situation shown above and below.

Looking at our example again, it’s evident that your identical by chance (IBC) match’s A locations (1, 3, 5, 7 & 9) will match your Mom. C locations (2, 4, 6 8, & 10) will match your Dad, but the nonmatching segments interleaved in-between that match alternating parents will prevent your match from matching either of your parents. In other words, out of 10 contiguous locations in our example, your IBC match has 5 As alternated with 5 Cs, so they won’t match either of your parents who have 10 As or 10 Cs in a row.

This recombination effect can work in either direction. Either or both matching people’s DNA could be randomly mixed causing them to match each other, but not their parents.

Regardless of whose DNA is zigzagging back and forth between maternal and paternal, the match is not genealogical and does not confirm a common ancestor.

This is exactly why triangulation works and is crucial.

If you legitimately match a third person, shown below, on your maternal side, they will match you, your first legitimate maternal match, and your Mom because they carry all As. But they WON’T match the person who is matching you because they are identical by chance, shown in grey below.

The only person your identical by chance match matches in this group is you because they match you because of the chance recombination of parental DNA.

That third person WILL also match all other legitimate maternal matches on this segment.

In the graphic above, we see that while the grey identical by chance person matches you because of the random combination of As from your mother and Cs from your father, your legitimate maternal matches won’t match your identical by chance match.

This is the first step in identifying false matches.

Parental Cross-Matching

Removing the identical by chance match, and adding in the parents of your legitimate maternal match, we see that your maternal match, above, matches you because you both have all As inherited from one parent, not from a combination of both parents.

We know that because we can see the DNA of both parents of both matches in this example.

The ideal situation occurs when two people match and they have both had their parents tested. We need to see if each person matches the other person’s parents.

We can see that you do NOT match your match’s father and your match does NOT match your father.

You do match your match’s mother and your match does match your mother. I refer to this as Parental Cross-matching.

Your legitimate maternal matches will also match each other and your mother if she is available for testing.

All the people in yellow match each other, while the two parents in gray do not match any of your matches. An entire group of legitimate maternal matches on this segment, no matter how many, will all match each other.

If another person matches you and the other yellow people, you’ll still need to see if you match their parents, because if not, that means they are matching you on all As because their two parents DNA combined just happened, by chance, to contribute an A in all of those positions.

In this last example, your new match, in green, matches you, your legitimate match and both of your mothers, BUT, none of the four yellow people match either of the new match’s parents. You can see that the new green match inherited their As from the DNA of their mother and father both, randomly zigzagging back and forth.

The four yellow matches phase parentally as we just proved with cross matching to parents. The new match at first glance appears to be a legitimate match because they match all of the yellow people – but they aren’t because the yellow people don’t match the green person’s parents.

To tell the difference between legitimate matches and identical by chance matches, you need two things, in order.

  • Parental matching known as parental phasing along with parental cross-matching, if possible, AND
  • Legitimate identical by descent (IBD) triangulated matches

If you have the ability to perform parental matching, called phasing, that’s the easiest first step in eliminating identical by chance matches. However, few match pairs will have parents for everyone. You can use triangulation without parental phasing if parents aren’t available.

Let’s talk about both, including when and how close relatives can and cannot be used.

Parental Phasing

The technique of confirming your match to be legitimate by your match also matching one of your parents is called parental phasing.

If we have the parents of both people in a match pair available for matching, we can easily tell if the match does NOT match either parent. That’s Parental Cross Matching. If either match does NOT match one of the other person’s parents, the match is identical by chance, also known as a false positive.

See how easy that was!

If you, for example, is the only person in your match pair to have parents available, then you can parentally phase the match on your side if your match matches your parents. However, because your match’s parents are unavailable, your match to them cannon tbe verified as legitimate on their side. So you are not phased to their parents.

If you only have one of your parents available for matching, and your match does not match that parent, you CANNOT presume that because your match does NOT match that parent, the match is a legitimate match for the other, missing, parent.

There are four possible match conditions:

  • Maternal match
  • Paternal match
  • Matches neither parent which means the match is identical by chance meaning a false positive
  • Matches both parents in the case of pedigree collapse or endogamy

If two matching people do match one parent of both matches (parental cross-matching), then the match is legitimate. In other words, if we match, I need to match one of your parents and you need to match one of mine.

It’s important to compare your matches’ DNA to generationally older direct family members such as parents or grandparents, if that’s possible. If your grandparents are available, it’s possible to phase your matches back another generation.

Automatic Phasing at FamilyTreeDNA

FamilyTreeDNA automatically phases your matches to your parents if you test that parent, create or upload a GEDCOM file, and link your test and theirs to your tree in the proper places.

FamilyTreeDNA‘s Family Matching assigns or “buckets” your matches maternally and paternally. Matches are assigned as maternal or paternal matches if one or both parents have tested.

Additionally, FamilyTreeDNA uses triangulated matches from other linked relatives within your tree even if your parents have not tested. If you don’t have your parents, the more people you identify and link to your tree in the proper place, the more people will be assigned to maternal and paternal buckets. FamilyTreeDNA is the only vendor that does this. I wrote about this process in the article, Triangulation in Action at Family Tree DNA.

Parental Phasing Caveats

There are very rare instances where parental phasing may be technically accurate, but not genealogically relevant. By this, I mean that a parent may actually match one of your matches due to endogamy or a population level match, even if it’s considered a false positive because it’s not relevant in a genealogical timeframe.

Conversely, a parent may not match when the segment is actually legitimate, but it’s quite rare and only when pedigree collapse has occurred in a very specific set of circumstances where both parents share a common ancestor.

Let’s take a look at that.

Pedigree Collapse

It’s not terribly uncommon in the not-too-distant past to find first cousins marrying each other, especially in rather closely-knit religious communities. I encounter this in Brethren, Mennonite and Amish families often where the community was small and out-marrying was frowned upon and highly discouraged. These families and sometimes entire church congregations migrated cross-country together for generations.

When pedigree collapse is present, meaning the mother and father share a common ancestor not far in the past, it is possible to inherit half of one segment from Mom and the other half from Dad where those halves originated with the same ancestral couple.

For example, let’s say the matching segment between you and your match is 12 cM in length, shown below. You inherited the blue segment from your Dad and the neighboring peach segment from Mom – shown just below the segment numbers. You received 6 cM from both parents.

Another person’s DNA does match you, shown in the bottom row, but they are not shown on the DNA match list of either of your parents. That’s because the DNA segments of the parents just happened to recombine in 6 cM pieces, respectively, which is below the 7 cM matching threshold of the vendor in this example.

If the person matched you at 12 cM where you inherited 8 cM from one parent and 4 from the other, that person would show on one parent’s match list, but not the other. They would not be on the parent’s match list who contributed only 4 cM simply because the DNA divided and recombined in that manner. They would match you on a longer segment than they match your parent at 8 cM which you might notice as “odd.”

Let’s look at another example.

click to enlarge image

If the matching segment is 20 cM, the person will match you and both of your parents on different pieces of the same segment, given that both segments are above 7 cM. In this case, your match who matches you at 20 cM will match each of your parents at 10 cM.

You would be able to tell that the end location of Dad’s segment is the same as the start location of Mom’s segment.

This is NOT common and is NOT the “go to” answer when you think someone “should” match your parent and does not. It may be worth considering in known pedigree collapse situations.

You can see why someone observing this phenomenon could “presume” that DNA skipped a generation because the person matches you on segments where they don’t match your parent. But DNA didn’t skip anything at all. This circumstance was caused by a combination of pedigree collapse, random division of DNA, then random recombination in the same location where that same DNA segment was divided earlier. Clearly, this sequence of events is not something that happens often.

If you’ve uploaded your DNA to GEDmatch, you can select the “Are your parents related?” function which scans your DNA file for runs of homozygosity (ROH) where your DNA is exactly the same in both parental locations for a significant distance. This suggests that because you inherited the exact same sequence from both parents, that your parents share an ancestor.

If your parents didn’t inherit the same segment of DNA from both parents, or the segment is too short, then they won’t show as “being related,” even if they do share a common ancestor.

Now, let’s look at the opposite situation. Parental phasing and ROH sometimes do occur when common ancestors are far back in time and the match is not genealogically relevant.


I often see non-genealogical matching occur when dealing with endogamy. Endogamy occurs when an entire population has been isolated genetically for a long time. In this circumstance, a substantial part of the population shares common DNA segments because there were few original population founders. Much of the present-day population carries that same DNA. Many people within that population would match on that segment. Think about the Jewish community and indigenous Americans.

Consider our original example, but this time where much of the endogamous population carries all As in these positions because one of the original founders carried that nucleotide sequence. Many people would match lots of other people regardless of whether they are a close relative or share a distant ancestor.

People with endogamous lines do share relatives, but that matching DNA segment originated in ancestors much further back in time. When dealing with endogamy, I use parental phasing as a first step, if possible, then focus on larger matches, generally 20 cM or greater. Smaller matches either aren’t relevant or you often can’t tell if/how they are.

At FamilyTreeDNA, people with endogamy will find many people bucketed on the “Both” tab meaning they triangulate with people linked on both sides of the tester’s tree.

An example of a Jewish person’s bucketed matches based on triangulation with relatives linked in their tree is shown above.

Your siblings, their children, and your children will be related on both your mother’s and father’s sides, but other people typically won’t be unless you have experienced either pedigree collapse where you are related both maternally and paternally through the same ancestors or you descend from an endogamous population.

How Many Identical-by-Chance Matches Will I Have?

If you have both parents available to test, and you’re not dealing with either pedigree collapse or endogamy, you’ll likely find that about 15-20% of your matches don’t match your parents on the same segment and are identical by chance.

With endogamy, you’ll have MANY more matches on your endogamous lines and you’ll have some irrelevant matches, often referred to as “false positive” matches even though they technically aren’t, even using parental phasing.

Your Parents Have DNA That You Don’t

Sometimes people are confused when reviewing their matches and their parent’s match to the same person, especially when they match someone and their parent matches them on a different or an additional segment.

If you match someone on a specific segment and your parents do not, that’s a false positive FOR THAT SEGMENT. Every segment has its own individual history and should be evaluated individually. You can match someone on two segments, one from each parent. Or three segments, one from each parent and one that’s identical by chance. Don’t assume.

Often, your match will match both you and your parent on the same segment – which is a legitimate parentally phased match.

But what if your match matches your parent on a different segment where they don’t match you? That’s a false positive match for you.

Keep in mind that it is possible for one of your matches to match your parent on a separate or an additional segment that IS legitimate. You simply didn’t inherit that particular segment from your parent.

That’s NOT the same situation as someone matching you that does NOT match one of your parents on the same segment – which is an identical by chance or false match.

Your parent having a match that does not match you is the reverse situation.

I have several situations where I match someone on one segment, and they match my parent on the same segment. Additionally, that person matches my parent on another segment that I did NOT inherit from that parent. That’s perfectly normal.

Remember, you only inherit half of your parent’s DNA, so you literally did NOT inherit the other half of their DNA. Your mother, for example, should have twice as many matches as you on her side because roughly half of her matches won’t match you.

That’s exactly why testing your parents and close family members is so critical. Their matches are as valid and relevant to your genealogy as your own. The same is true for other relatives, such as aunts and uncles with whom you share ALL of the same ancestors.

You need to work with your family member’s matches that you don’t share.

No DNA Match Doesn’t Mean You’re Not Related

Some people think that not matching someone on a DNA test is equivalent to saying they aren’t related. Not sharing DNA doesn’t mean you’re not related.

People are often disappointed when they don’t match someone they think they should and interpret that to mean that the testing company is telling them they “aren’t related.” They are upset and take issue with this characterization. But that’s not what it means.

Let’s analyze this a bit further.

First, not sharing DNA with a second cousin once removed (2C1R) or more distant does NOT mean you’re NOT related to that person. It simply means you don’t share any measurable DNA ABOVE THE VENDOR THRESHOLD.

All known second cousins match, but about 10% of third cousins don’t match, and so forth on up the line with each generation further back in time having fewer cousins that match each other.

If you have tested close relatives, check to see if that cousin matches your relatives.

Second, it’s possible to match through the “other” or unexpected parent. I certainly didn’t think this would be the case in my family, because my father is from Appalachia and my mother’s family is primarily from the Netherlands, Germany, Canada, and New England. But I was wrong.

All it took was one German son that settled in Appalachia, and voila, a match through my mother that I surely thought should have been through my father’s side. I have my mother’s DNA and sure enough, my match that I thought should be on my father’s side matches Mom on the same segment where they match me, along with several triangulated matches. Further research confirmed why.

I’ve also encountered situations where I legitimately match someone on both my mother’s and father’s side, on different segments.

Third, imputation can be important for people who don’t match and think they should. Imputation can also cause matching segment length to be overreported.

Ok, so what’s imputation and why do I care?


Every DNA vendor today has to use some type of imputation.

Let me explain, in general, what imputation is and why vendors use it.

Over the years, DNA processing vendors who sell DNA chips to testing companies have changed their DNA chips pretty substantially. While genealogical autosomal tests test about 700,000 DNA locations, plus or minus, those locations have changed over time. Today, some of these chips only have 100,000 or so chip locations in common with chips either currently or previously utilized by other vendors.

The vendors who do NOT accept uploads, such as 23andMe or Ancestry, have to develop methods to make their newest customers on their DNA processing vendor’s latest chip compatible with their first customer who was tested on their oldest chip – and all iterations in-between.

Vendors who do accept transfers/uploads from other vendors have to equalize any number of vendors’ chips when their customers upload those files.

Imputation is the scientific way to achieve this cross-platform functionality and has been widely used in the industry since 2017.

Imputation, in essence, fills in the blanks between tested locations with the “most likely” DNA found in the human population based on what’s surrounding the blank location.

Think of the word C_T. There are a limited number of letters and words that are candidates for C_T. If you use the word in a sentence, your odds of accuracy increase dramatically. Think of a genetic string of nucleotides as a sentence.

Imputation can be incorrect and can cause both false positive and false negative matches.

For the most part, imputation does not affect close family matches as much as more distant matches. In other words, imputation is NOT going to cause close family members not to match.

Imputation may cause more distant family members not to match, or to have a false positive match when imputation is incorrect.

Imputation is actually MUCH less problematic than I initially expected.

The most likely effect of imputation is to cause a match to be just above or below the vendor threshold.

How can we minimize the effects of imputation?

  • Generally, the best result will be achieved if both people test at the same vendor where their DNA is processed on the same chip and less imputation is required.
  • Upload the results of both people to both MyHeritage and FamilyTreeDNA. If your match results are generally consistent at those vendors, imputation is not a factor.
  • GEDmatch does not use imputation but attempts to overcome files with low overlapping regions by allowing larger mismatch areas. I find their matches to be less accurate than at the various vendors.

Additionally, Ancestry has a few complicating factors.

Ancestry Issues

AncestryDNA is different in three ways.

  • Ancestry doesn’t provide segment information so it’s impossible to triangulate or identify the segment or chromosome where people match. There is no chromosome browser or triangulation tool.
  • Ancestry down-weights and removes some segments in areas where they feel that people are “too matchy.” You can read Ancestry’s white papers here and here.

These “personal pileup regions,” as they are known, can be important genealogically. In my case, these are my mother’s Acadian ancestors. Yes, this is an endogamous population and also suffers from pedigree collapse, but since this is only one of my mother’s great-grandparents, this match information is useful and should not be removed.

  • Ancestry doesn’t show matches in common if the shared segments are less than 20cM. Therefore, you may not see someone on a shared match list with a relative when they actually are a shared match.

If two people both match a third person on less than a 20 cM segment at Ancestry, the third person won’t appear on the other person’s shared match list. So, if I match John Doe on 19 cM of DNA, and I looked at the shared matches with my Dad, John Doe does NOT appear on the shared match list of me and my Dad – even though he is a match to both of us at 19 cM.

The only way to determine if John Doe is a shared match is to check my Dad’s and my match list individually, which means Dad and I will need to individually search for John Doe.

Caveat here – Ancestry’s search sometimes does not work correctly.

Might someone who doesn’t understand that the shared match list doesn’t show everyone who shares DNA with both people presume that the ancestral DNA of that ancestor “skipped a generation” because John Doe matches me with a known ancestor, and not Dad on our shared match list? I mean, wouldn’t you think that a shared match would be shown on a tab labeled “Shared Matches,” especially since there is no disclaimer?

Yes, people can be forgiven for believing that somehow DNA “skipped” a generation in this circumstance, especially if they are relatively inexperienced and they don’t understand Ancestry’s anomalies or know that they need to or how to search for matches individually.

Even if John Doe does match me and Dad both, we still need to confirm that it’s on the same segment AND it’s a legitimate match, not IBC. You can’t perform either of these functions at Ancestry, but you can elsewhere.

Ancestry WorkArounds

To obtain this functionality, people can upload their DNA files for free to both FamilyTreeDNA and MyHeritage, companies that do provide full shared DNA reporting (in common with) lists of ALL matches and do provide segment information with chromosome browsers. Furthermore, both provide triangulation in different ways.

Matching is free, but an inexpensive unlock is required at both vendors to access advanced tools such as Family Matching (bucketing) and triangulation at Family Tree DNA and phasing/triangulation at MyHeritage.

I wrote about Triangulation in Action at FamilyTreeDNA, here.

MyHeritage actually brackets triangulated segments for customers on their chromosome browser, including parents, so you get triangulation and parental phasing at the same time if you and your parent have both tested or uploaded your DNA file to MyHeritage. You can upload, for free, here.

In this example, my mother is matching to me in red on the entire length of chromosome 18, of course, and three other maternal cousins triangulate with me and mother inside the bracketed portion of chromosome 18. Please note that if any one of the people included in the chromosome browser comparison do not triangulate, no bracket is drawn around any others who do triangulate. It’s all or nothing. I remove people one by one to see if people triangulate – or build one by one with my mother included.

I wrote about Triangulation in Action at MyHeritage, here.

People can also upload to GEDmatch, a third-party site. While GEDmatch is less reliable for matching, you can adjust your search thresholds which you cannot do at other vendors. I don’t recommend routinely working below 7 cM. I occasionally use GEDmatch to see if a pedigree collapse segment has recombined below another vendor’s segment matching threshold.

Do NOT check the box to prevent hard breaks when selecting the One-to-One comparison. Checking that box allows GEDmatch to combine smaller matching segments into mega-segments for matching.

I wrote about Triangulation in Action at GEDmatch, here.

Transferring/Uploading Your DNA 

If you want to transfer your DNA to one of these vendors, you must download the DNA file from one vendor and upload it to another. That process does NOT remove your DNA file from the vendor where you tested, unless you select that option entirely separately.

I wrote full step-by-step transfer/upload instructions for each vendor, here.

Testing Close Relatives Is VERY Useful – Just Not for Triangulation

Of course, your best bet if you don’t have your parents available to test is to test as many of your grandparents, great-aunts/uncles, aunts, and uncles as possible. Test your siblings as well, because they will have inherited some of the same and some different segments of DNA from your parents – which means they carry different pieces of your ancestors’ DNA.

Just because close relatives don’t make good triangulation candidates doesn’t mean they aren’t valuable. Close relatives are golden because when they DO share a match with you, you know where to start looking for a common ancestor, even if your relative matches that person on a different segment than you do.

Close relatives are also important because they will share pieces of your common ancestor’s DNA that you don’t. Their matches can unlock the answers to your genealogy questions.

Ok, back to triangulation.

Triangulated Matches

A triangulated match is, of course, when three people all descended from a common ancestor and match each other on the same segment of DNA.

That means all three people’s DNA matches each other on that same segment, confirming that the match is not by chance, and that segment did descend from a common ancestor or ancestral couple.

But, is this always true? You’re going to hate this answer…

“It depends.”

You knew that was coming, didn’t you! 😊

It depends on the circumstances and relationships of the three people involved.

  • One of those three people can match the other two by chance, not by descent, especially if two of those people are close relatives to each other.
  • Identical by chance means that one of you didn’t inherit that DNA from one single parent. That zigzag phenomenon.
  • Furthermore, triangulated DNA is only valid as far back as the closest common ancestor of any two of the three people.

Let’s explore some examples.

Building Triangulation Evidence – Ingredients and a Recipe

The strongest case of triangulation is when:

  • You and at least two additional cousins match on the same segment AND
  • Descend through different children of the common ancestral couple

Let’s look at a valid triangulated match.

In this first example, the magenta segment of DNA is at least partially shared by four of the six cousins and triangulates to their common great-grandfather. Let’s say that these cousins then match with two other people descended from different children of their great-great-great-grandparents on this same segment. Then the entire triangulation group will have confirmed that segment’s origin and push the descent of that segment back another two generations.

These people all coalesce into one line with their common great-grandparents.

I’m only showing 3 generations in this triangulated match, but the concept is the same no matter how many generations you reach back in time. Although, over time, segments inherited from any specific ancestor become smaller and smaller until they are no longer passed to the next generation.

In this pedigree chart, we’re only tracking the magenta DNA which is passed generation to generation in descendants.

Eventually, of course, those segments become smaller and indistinguishable as they either aren’t passed on at all or drop below vendor matching thresholds.

This chart shows the average amount of DNA you would carry from each generational ancestor. You inherit half of each parent’s DNA, but back further than that, you don’t receive exactly half of any ancestor’s DNA in any generation. Larger segments are generally cut in two and passed on partially, but smaller segments are often either passed on whole or not at all.

On average, you’ll carry 7 cM of your eight-times-great-grandparents. In reality, you may carry more or you may not carry any – and you are unlikely to carry the same segment as any random other descendants but we know it happens and you’ll find them if enough (or the right) descendants test.

Putting this another way, if you divide all of your approximate 7000 cM of DNA into 7 cM segments of equal length – you’ll have 1000 7 cM segments. So will every other descendant of your eight-times-great-grandparent. You can see how small the chances are of you both inheriting that same exact 7 cM segment through ten inheritance/transmission events, each. Yet it does happen.

I have several triangulated matches with descendants of Charles Dodson and his wife, Anne through multiple of their 9 (or so) children, ten generations back in my tree. Those triangulated matches range from 7-38 cM. It’s possible that those three largest matches at 38 cM could be related through multiple ancestors because we all have holes in our trees – including Anne’s surname.

Click to enlarge image

It helps immensely that Charles Dodson had several children who were quite prolific as well.

Of course, the further back in time, the more “proof” is necessary to eliminate other unknown common ancestors. This is exactly why matching through different children is important for triangulation and ancestor confirmation.

The method we use to confirm the common ancestor is that all of the descendants who match the tester on the same segment all also match each other. This greatly reduces the chances that these people are matching by chance. The more people in the triangulation group, the stronger the evidence. Of course, parental phasing or cross-matching, where available is an added confirmation bonus.

In our magenta inheritance example, we saw that three of the males and one of the females from three different descendants of the great-grandparents all carry at least a portion of that magenta segment of great-grandpa’s DNA.

Now, let’s take a look at a different scenario.

Why can’t siblings or close relatives be used as two of the three people needed for triangulation?

Aunts and Uncles

We know that the best way to determine if a match is valid is by parental phasing – your match also matching to one of your parents.

If both parents aren’t available, looking for close family matches in common with your match is the next hint that genealogists seek.

Let’s say that you and your match both match your aunt or uncle in common or their children.

You and your aunts or uncles matching DNA only pushes your common ancestor back to your grandparents.

At that point, your match is in essence matching to a segment that belongs to your grandparents. Your matches’ DNA, or your grandparents’ DNA could have randomly recombined and you and your aunt/cousins could be matching that third person by chance.

Ok, then, what about siblings?


The most recent common ancestor (MRCA) of you and someone who also matches your sibling is your parents. Therefore, you and your sibling actually only count as one “person” in this scenario. In essence, it’s the DNA of your parent(s) that is matching that third person, so it’s not true triangulation. It’s the same situation as above with aunts/uncles, except the common ancestor is closer than your grandparents.

The DNA of your parents could have recombined in both siblings to look like a match to your match’s family. Or vice versa. Remember Parental Cross-Matching.

If you and a sibling inherited EXACTLY the same segment of your Mom’s and Dad’s DNA, and you match someone by chance – that person will match your sibling by chance as well.

In this example, you can see that both siblings 1 and 2 inherited the exact same segments of DNA at the same locations from both of their parents.

Of course, they also inherited segments at different locations that we’re not looking at that won’t match exactly between siblings, unless they are identical twins. But in this case, the inherited segments of both siblings will match someone whose DNA randomly combined with green or magenta dots in these positions to match a cross-section of both parents.

How False Positives Work and How to Avoid Them

We saw in our first example, displayed again above, what a valid triangulated match looks like. Now let’s expand this view and take a look more specifically at how false positive matches occur.

On the left-hand (blue) side of this graphic, we see four siblings that descend through their father from Great-grandpa who contributed that large magenta segment of DNA. That segment becomes reduced in descendants in subsequent generations.

In downstream generations, we can see gold, white and green segments being added to the DNA inherited by the four children from their ancestor’s spouses. Dad’s DNA is shown on the left side of each child, and Mom’s on the right.

  • Blue Children 1 and 2 inherited the same segments of DNA from Mom and Dad. Magenta from Dad and green from Mom.
  • Blue Child 3 inherited two magenta segments from Dad in positions 1 and 2 and one gold segment from Dad in position 3. They inherited all white segments from Mom.
  • Blue Child 4 inherited all gold segments from Dad and all white segments from Mom.

The family on the blue left-hand side is NOT related to the pink family shown at right. That’s important to remember.

I’ve intentionally constructed this graphic so that you can see several identical by chance (IBC) matches.

Child 5, the first pink sibling carries a white segment in position 1 from Dad and gold segments in positions 2 and 3 from Dad. From Mom, they inherited a green segment in position 1, magenta in position 2 and green in position 3.

IBC Match 1 – Looking at the blue siblings, we see that based on the DNA inherited from Pink Child 5’s parents, Pink Child 5 matches Blue Child 4 with white, gold and gold in positions 1-3, even though they weren’t inherited from the same parent in Blue Child 4. I circled this match in blue.

IBC Match 2 – Pink Child 5 also matches Blue Children 1 and 2 (red circles) because Pink Child 5 has green, magenta, and green in positions 1-3 and so do Blue Children 1 and 2. However, Blue Children 1 and 2 inherited the green and magenta segments from Mom and Dad respectively, not just from one parent.

Pink Child 5 matches Blue Children 1, 2 and 4, but not because they match by descent, but because their DNA zigzags back and forth between the blue children’s DNA contributed by both parents.

Therefore, while Pink Child 5 matches three of the Blue Children, they do not match either parent of the Blue Children.

IBC Match 3 – Pink Child 6 matches Blue Child 3 with white, magenta and gold in positions 1-3 based on the same colors of dots in those same positions found in Blue Child 3 – but inherited both paternally and maternally.

You can see that if we had the four parents available to test, that none of the Pink Children would match either the Blue Children’s mother or father and none of the Blue Children would match either of the Pink Children’s mother or father.

This is why we can’t use either siblings or close family relatives for triangulation.

Distant Cousins Are Best for Triangulation & Here’s Why

When triangulating with 3 people, the most recent common ancestor (MRCA) intersection of the closest two people is the place at which triangulation turns into only two lines being compared and ceases being triangulation. Triangle means 3.

If siblings are 2 of the 3 matching people, then their parents are essentially being compared to the third person.

If you, your aunt/uncle, and a third person match, your grandparents are the place in your tree where three lines converge into two.

The same holds true if you’re matching against a sibling pair on your match’s side, or a match and their aunt/uncle, etc.

The further back in your tree you can push that MRCA intersection, the more your triangulated match provides confirming evidence of a common ancestor and that the match is valid and not caused by random recombination.

That’s exactly what the descendants of Charles Dodson have been able to do through triangulation with multiple descendants from several of his children.

It’s also worth mentioning at this point that the reason autosomal DNA testing uses hundreds/thousands of base pairs in a comparison window and not 3 or 6 dots like in my example is that the probability of longer segments of DNA simply randomly matching by chance is reduced with length and SNP density which is the number of SNP locations tested within that cM range.

Hence a 7 cM/500 SNP minimum is the combined rule of thumb. At that level, roughly half of your matches will be valid and half will be identical by chance unless you’re dealing with endogamy. Then, raise your threshold accordingly.

Ok, So Where are We? A Triangulation Checklist for You!

I know this has been a relatively long educational article, but it’s important to really understand that testing close relatives is VERY important, but also why we can’t effectively use them for triangulation.

Here’s a handy-dandy summary matching/triangulation checklist for you to use as you work through your matches.

  • You inherit half of each of your parents’ DNA. There is no other place for you to obtain or inherit your DNA. There is no DNA fairy sprinkling you with DNA from another source:)
  • DNA does NOT skip generations, although in occasional rare circumstances, it may appear that this happened. In this situation, it’s incumbent upon you, the genealogist, to PROVE that an exception has occurred if you really believe it has. Those circumstances might be pedigree collapse or perhaps imputation. You’ll need to compare matches at vendors who provide a chromosome browser, triangulation, and full shared match list information. Never assume that you are the exception without hard and fast proof. We all know about assume, right?
  • Your siblings inherit half of your parents’ DNA too, but not the same exact half of your parent’s DNA that you other siblings did (unless they are identical twins.) You may inherit the exact same DNA from either or both of your parents on certain segments.
  • Your matches may match your parents on different or an additional segment that you did not inherit.
  • Every segment has an individual history. Evaluate every matching segment separately. One matching segment with someone could be maternal, one paternal, and one identical by chance.
  • You can confirm matches as valid if your match matches one of your parents, and you match one of your match’s parents. Parental Phasing is when your match matches your parent. Parental Cross-Matching is when you both match one of each other’s parents. To be complete, both people who match each other need to match one of the parents of the other person. This rule still holds even if you have a known common ancestor. I can’t even begin to tell you how many times I’ve been fooled.
  • 15-20% (or more with endogamy) of your matches will be identical by chance because either your DNA or your match’s DNA aligns in such a way that while they match you, they don’t match either of your parents.
  • Your siblings, aunts, and uncles will often inherit the same DNA as you – which means that identical by chance matches will also match them. That’s why we don’t use close family members for triangulation. We do utilize close family members to generate common match hints. (Remember the 20 cM shared match caveat at Ancestry)
  • While your siblings, aunts, and uncles are too close to use for triangulation, they are wonderful to identify ancestral matches. Some of their matches will match you as well, and some will not because your close family members inherited segments of your ancestor’s DNA that you did not. Everyone should test their oldest family members.
  • Triangulate your close family member’s matches separately from your own to shed more light on your ancestors.
  • Endogamy may interfere with parental phasing, meaning you may match because you and/or your match may have inherited some of the same DNA segment(s) from both sides of your tree and/or more DNA than might otherwise be expected.
  • Pedigree collapse needs to be considered when using parental phasing, especially when the same ancestor appears on both sides of your family tree. You may share more DNA with a match than expected.
  • Conversely, with pedigree collapse, your match may not match your parents, or vice versa, if a segment happens to have recombined in you in a way that drops the matching segments of your parents beneath the vendor’s match threshold.
  • While you will match all of your second cousins, you will only match approximately 90% of your third cousins and proportionally fewer as your relationship reaches further back in time.
  • Not being a DNA match with someone does NOT mean you’re NOT related to them, unless of course, you’re a second cousin (2C) or closer. It simply means you don’t carry any common ancestral segments above vendor thresholds.
  • At 2C or closer, if you’re not a DNA match, other alternative situations need to be considered – including the transfer/upload of the wrong person’s DNA file.
  • Imputation, a scientific process required of vendors may interfere with matching, especially in more distant relatives who have tested on different platforms.
  • Imputation artifacts will be less obvious when people are more closely related, meaning closer relatives can be expected to match on more and larger segments and imputation errors make less difference.
  • Imputation will not cause close relatives, meaning 2C or closer, to not match each other.
  • In addition to not supporting segment matching information, Ancestry down-weights some segments, removes some matching DNA, and does not show shared matches below 20cM, causing some people to misinterpret their lack of common matches in various ways.
  • To resolve questions about matching issues at Ancestry, testers can transfer/upload their DNA files to MyHeritage, FamilyTreeDNA, and GEDmatch and look for consistent matches on the same segment. Start and end locations may vary to some extent between vendors, but the segment size should be basically in the same location and roughly the same size.
  • GEDmatch does not use imputation but allows larger non-matching segments to combine as a single segment which sometimes causes extremely “generous” matches. GEDmatch matching is less reliable than FamilyTreeDNA or MyHeritage, but you can adjust the matching thresholds.
  • The best situation for matching is for both people to test at the same vendor who supports and provides segment data and a chromosome browser such as 23andMe, FamilyTreeDNA, or MyHeritage.
  • Siblings cannot be used for triangulation because the most recent common ancestor (MRCA) between you and your siblings is your parents. Therefore, the “three” people in the triangulation group is reduced to two lines immediately.
  • Uncles and aunts should not be used for triangulation because the most recent common ancestors between you and your aunts and uncles are your grandparents.
  • Conversely, you should not consider triangulating with siblings and close family members of your matches as proof of an ancestral relationship.
  • A triangulation group of 3 people is only confirmation as far back as when two of those people’s lines converge and reach a common ancestor.
  • Identical by chance (IBC) matching occurs when DNA from the maternal and paternal sides are mixed positionally in the child to resemble a maternal/paternal side match with someone else.
  • Identical by chance DNA admixture (when compared to a match) could have occurred in your parents or grandparent’s generation, or earlier, so the further back in time that people in a triangulation group reach, the more reliable the triangulation group is likely to be.
  • The larger the segments and/or the triangulation group, the stronger the evidence for a specific confirmed common ancestor.
  • Early families with a very large number of descendants may have many matching and triangulated members, even 9 or 10 generations later.
  • While exactly 50% of each ancestor’s DNA is not passed in each generation, on average, you will carry 7 cM of your ancestors 10 generations back in your tree. However, you may carry more, or none.
  • The percentage of matching descendants decreases with each generation beyond great-grandparents.
  • The ideal situation for triangulation is a significant number of people, greater than three, who match on the same reasonably sized segment (7 cM/500 SNP or larger) and descend from the same ancestor (or ancestral couple) through different children whose spouses in descendant generations are not also related.
  • This means that tree completion is an important factor in match/triangulation reliability.
  • Triangulating through different children of the ancestral couple makes it significantly less likely that a different unknown common ancestor is contributing that segment of DNA – like an unknown wife in a descendant generation.


The Bottom Line

Here’s the bottom line.

  1. Don’t use close relatives to triangulate.
  2. Use parents for Parental Phasing.
  3. Use Parental Cross-Matching when possible.
  4. Use close relatives to look for shared common matches that may lead to triangulation possibilities.
  5. Triangulate your close relatives’ DNA in addition to your own for bonus genealogical information. They will match people that you don’t.
  6. For the most reliable triangulation results, use the most distant relatives possible, descended through different children of the common ancestral couple.
  7. Keep this checklist of best practices, cautions, and caveats handy and check the list as necessary when evaluating the strength of any match or triangulation group. It serves as a good reminder for what to check if something seems “off” or unusual.

Feel free to share and pass this article (and checklist) on to your genealogy buddies and matches as you explain triangulation and collaborate on your genealogy.

Have fun!!!



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Ancient DNA Matches – What Do They Mean?

The good news is that my three articles about the Anzick and other ancient DNA of the past few days have generated a lot of interest.

The bad news is that it has generated hundreds of e-mails every day – and I can’t possibly answer them all personally.  So, if you’ve written me and I don’t reply, I apologize and  I hope you’ll understand.  Many of the questions I’ve received are similar in nature and I’m going to answer them in this article.  In essence, people who have matches want to know what they mean.

Q – I had a match at GedMatch to <fill in the blank ancient DNA sample name> and I want to know if this is valid.

A – Generally, when someone asks if an autosomal match is “valid,” what they really mean is whether or not this is a genealogically relevant match or if it’s what is typically referred to as IBS, or identical by state.  Genealogically relevant samples are referred to as IBD, or identical by descent.  I wrote about that in this article with a full explanation and examples, but let me do a brief recap here.

In genealogy terms, IBD is typically used to mean matches over a particular threshold that can be or are GENEALOGICALLY RELEVANT.  Those last two words are the clue here.  In other words, we can match them with an ancestor with some genealogy work and triangulation.  If the segment is large, and by that I mean significantly over the threshold of 700 SNPs and 7cM, even if we can’t identify the common ancestor with another person, the segment is presumed to be IBD simply because of the math involved with the breakdown of segment into pieces.  In other words, a large segment match generally means a relatively recent ancestor and a smaller segment means a more distant ancestor.  You can readily see this breakdown on this ISOGG page detailing autosomal DNA transmission and breakdown.

Unfortunately, often smaller segments, or ones determined to be IBS are considered to be useless, but they aren’t, as I’ve demonstrated several times when utilizing them for matching to distant ancestors.  That aside, there are two kinds of IBS segments.

One kind of IBS segment is where you do indeed share a common ancestor, but the segment is small and you can’t necessarily connect it to the ancestor.  These are known as population matches and are interpreted to mean your common ancestor comes from a common population with the other person, back in time, but you can’t find the common ancestor.  By population, we could mean something like Amish, Jewish or Native American, or a country like Germany or the Netherlands.

In the cases where I’ve utilized segments significantly under 7cM to triangulate ancestors, those segments would have been considered IBS until I mapped them to an ancestor, and then they suddenly fell into the IBD category.

As you can see, the definitions are a bit fluid and are really defined by the genealogy involved.

The second kind of IBS is where you really DON’T share an ancestor, but your DNA and your matches DNA has managed to mutate to a common state by convergence, or, where your Mom’s and Dad’s DNA combined form a pseudo match, where you match someone on a segment run long enough to be considered a match at a low level.  I discussed how this works, with examples, in this article.  Look at example four, “a false match.”

So, in a nutshell, if you know who your common ancestor is on a segment match with someone, you are IBD, identical by descent.  If you don’t know who your common ancestor is, and the segment is below the normal threshold, then you are generally considered to be IBS – although that may or may not always be true.  There is no way to know if you are truly IBS by population or IBS by convergence, with the possible exception of phased data.

Data phasing is when you can compare your autosomal DNA with one or both parents to determine which half you obtained from whom.  If you are a match by convergence where your DNA run matches that of someone else because the combination of your parents DNA happens to match their segment, phasing will show that clearly.  Here’s an example for only one location utilizing only my mother’s data phased with mine.  My father is deceased and we have to infer his results based on my mother’s and my own.  In other words, mine minus the part I inherited from my mother = my father’s DNA.

My Result My Result Mother’s Result Mother’s Result Father’s Inferred Result Father’s Inferred Result

In this example of just one location, you can see that I carry a T and an A in that location.  My mother carries a T and a G, so I obviously inherited the T from her because I don’t have a G.  Therefore, my father had to have carried at least an A, but we can’t discern his second value.

This example utilized only one location.  Your autosomal data file will hold between 500,000 and 700,000 location, depending on the vendor you tested with and the version level.

You can phase your DNA with that of your parent(s) at GedMatch.  However, if both of your parents are living, an easier test would be to see if either of your parents match the individual in question.  If neither of your parents match them, then your match is a result of convergence or a data read error.

So, this long conversation about IBD and IBS is to reach this conclusion.

All of the ancient specimens are just that, ancient, so by definition, you cannot find a genealogy match to them, so they are not IBD.  Best case, they are IBS by population.  Worse case, IBS by convergence.  You may or may not be able to tell the difference.  The reason, in my example earlier this week, that I utilized my mother’s DNA and only looked at locations where we both matched the ancient specimens was because I knew those matches were not by convergence – they were in fact IBS by population because my mother and I both matched Anzick.

ancient compare5

Q – What does this ancient match mean to me?

A – Doggone if I know.  No, I’m serious.  Let’s look at a couple possibilities, but they all have to do with the research you have, or have not, done.

If you’ve done what I’ve done, and you’ve mapped your DNA segments to specific ancestors, then you can compare your ancient matching segments to your ancestral spreadsheet map, especially if you can tell unquestionably which side the ancestral DNA matches.  In my case, shown above, the Clovis Anzik matched my mother and me on the same segment and we both matched Cousin Herbie.  We know unquestionably who our common ancestor is with cousin Herbie – so we know, in our family line, which line this segment of DNA shared with Anzick descends through.

ancient compare6

If you’re not doing ancestor mapping, then I guess the Anzick match would come in the category of, “well, isn’t that interesting.”  For some, this is a spiritual connection to the past, a genetic epiphany.  For other, it’s “so what.”

Maybe this is a good reason to start ancestor mapping!  This article tells you how to get started.

Q – Does my match to Anzick mean he is my ancestor?

A – No, it means that you and Anzick share common ancestry someplace back in time, perhaps tens of thousands of years ago.

Q – I match the Anzick sample.  Does this prove that I have Native American heritage? 

A – No, and it depends.  Don’t you just hate answers like this?

No, this match alone does not prove Native American heritage, especially not at IBS levels.  In fact, many people who don’t have Native heritage match small segments?  How can this be?  Well, refer to the IBS by convergence discussion above.  In addition, Anzick child came from an Asian population when his ancestors migrated, crossing from Asia via Beringia.  That Eurasian population also settled part of Europe – so you could be matching on very small segments from a common population in Eurasia long ago.  In a paper just last year, this was discussed when Siberian ancient DNA was shown to be related to both Native Americans and Europeans.

In some cases, a match to Anzick on a segment already attributed to a Native line can confirm or help to confirm that attribution.  In my case, I found the Anzick match on segments in the Lore family who descend from the Acadians who were admixed with the Micmac.  I have several Anzick match segments that fit that criteria.

A match to Anzick alone doesn’t prove anything, except that you match Anzick, which in and of itself is pretty cool.

Q – I’m European with no ancestors from America, and I match Anzick too.  How can that be?

A – That’s really quite amazing isn’t it.  Just this week in Nature, a new article was published discussing the three “tribes” that settled or founded the European populations.  This, combined with the Siberian ancient DNA results that connect the dots between an ancient population that contributed to both Europeans and Native Americans explains a lot.

3 European Tribes

If you think about it, this isn’t a lot different than the discovery that all Europeans carry some small amount of Neanderthal and Denisovan DNA.

Well, guess what….so does Anzick.

Here are his matches to the Altai Neanderthal.

Chr Start Location End Location Centimorgans (cM) SNPs
2 241484216 242399416 1.1 138
3 19333171 21041833 2.6 132
6 31655771 32889754 1.1 133

He does not match the Caucasus Neanderthal.  He does, however, match the Denisovan individual on one location.

Chr Start Location End Location Centimorgans (cM) SNPs
3 19333171 20792925 2.1 107

Q – Maybe the scientists are just wrong and the burial is not 12,500 years old,  maybe just 100 years old and that’s why the results are matching contemporary people.

A – I’m not an archaeologist, nor do I play one…but I have been closely involved with numerous archaeological excavations over the past decade with The Lost Colony Research Group, several of which recovered human remains.  The photo below is me with Anne Poole, my co-director, sifting at one of the digs.

anne and me on dig

There are very specific protocols that are followed during and following excavation and an error of this magnitude would be almost impossible to fathom.  It would require  kindergarten level incompetence on the part of not one, but all professionals involved.

In the Montana Anzick case, in the paper itself, the findings and protocols are both discussed.  First, the burial was discovered directly beneath the Clovis layer where more than 100 tools were found, and the Clovis layer was undisturbed, meaning that this is not a contemporary burial that was buried through the Clovis layer.  Second, the DNA fragmentation that occurs as DNA degrades correlated closely to what would be expected in that type of environment at the expected age based on the Clovis layer.  Third, the bones themselves were directly dated using XAD-collagen to 12,707-12,556 calendar years ago.  Lastly, if the remains were younger, the skeletal remains would match most closely with Native Americans of that region, and that isn’t the case.  This graphic from the paper shows that the closest matches are to South Americans, not North Americans.

anzick matches

This match pattern is also confirmed independently by the recent closest GedMatch matches to South Americans.

Q – How can this match from so long ago possibly be real?

A – That’s a great question and one that was terribly perplexing to Dr. Svante Paabo, the man who is responsible for producing the full genome sequence of the first, and now several more, Neanderthals.  The expectation was, understanding autosomal DNA gets watered down by 50% in every generation though recombination, that ancient genomes would be long gone and not present in modern populations.  Imagine Svante’s surprise when he discovered that not only isn’t true, but those ancient DNA segmetns are present in all Europeans and many Asians as well.  He too agonized over the question about how this is possible, which he discussed in this great video.  In fact he repeated these tests over and over in different ways because he was convinced that modern individuals could not carry Neanderthal DNA – but all those repeated tests did was to prove him right.  (Paabo’s book, Neanderthal Man, In Search of Lost Genomes is an incredible read that I would highly recommend.)

What this means is that the population at one time, and probably at several different times, had to be very small.  In fact, it’s very likely that many times different pockets of the human race was in great jeopardy of dying out.  We know about the ones that survived.  Probably many did perish leaving no descendants today.  For example, no Neanderthal mitochondrial DNA has been found in any living or recent human.

In a small population, let’s say 5 males and 5 females who some how got separated from their family group and founded a new group, by necessity.  In fact, this could well be a description of how the Native Americans crossed Beringia.  Those 5 males and 5 females are the founding population of the new group.  If they survive, all of the males will carry the men’s haplogroups – let’s say they are Q and C, and all of the descendants will carry the mitochondrial haplogroups of the females – let’s say A, B, C, D and X.

There is a very limited amount of autosomal DNA to pass around.  If all of those 10 people are entirely unrelated, which is virtually impossible, there will be only 10 possible combinations of DNA to be selected from.  Within a few generations, everyone will carry part of those 10 ancestor’s DNA.  We all have 8 ancestors at the great-grandparent level.  By the time those original settlers’ descendants had great-great-grandparents – of which each one had 16, at least 6 of those original people would be repeated twice in their tree.

There was only so much DNA to be passed around.  In time, some of the segments would no longer be able to be recombined because when you look at phasing, the parents DNA was exactly the same, example below.  This is what happens in endogamous populations.

My Result My Result Mother’s Result Mother’s Result Father’s Result Father’s  Result

Let’s say this group’s descendants lived without contact with other groups, for maybe 15,000 years in their new country.  That same DNA is still being passed around and around because there was no source for new DNA.  Mutations did occur from time to time, and those were also passed on, of course, but that was the only source of changed DNA – until they had contact with a new population.

When they had contact with a new population and admixture occurred, the normal 50% recombination/washout in every generation began – but for the previous 15,000 years, there had been no 50% shift because the DNA of the population was, in essence, all the same.  A study about the Ashkenazi Jews that suggests they had only a founding population of about 350 people 700 years ago was released this week – explaining why Ashkenazi Jewish descendants have thousands of autosomal matches and match almost everyone else who is Ashkenazi.  I hope that eventually scientists will do this same kind of study with Anzick and Native Americans.

If the “new population” we’ve been discussing was Native Americans, their males 15,000 year later would still carry haplogroups Q and C and the mitochondrial DNA would still be A, B, C, D and X.  Those haplogroups, and subgroups formed from mutations that occurred in their descendants, would come to define their population group.

In some cases, today, Anzick matches people who have virtually no non-Native admixture at the same level as if they were just a few generations removed, shown on the chart below.

anzick gedmatch one to all

Since, in essence, these people still haven’t admixed with a new population group, those same ancient DNA segments are being passed around intact, which tells us how incredibly inbred this original small population must have been.  This is known as a genetic bottleneck.

The admixture report below is for the first individual on the Anzick one to all Gedmatch compare at 700 SNPs and 7cM, above.  In essence, this currently living non-admixed individual still hasn’t met that new population group.


If this “new population” group was Neanderthal, perhaps they lived in small groups for tens of thousands of years, until they met people exiting Africa, or Denisovans, and admixed with them.

There weren’t a lot of people anyplace on the globe, so by virtue of necessity, everyone lived in small population groups.  Looking at the odds of survival, it’s amazing that any of us are here today.

But, we are, and we carry the remains, the remnants of those precious ancestors, the Denisovans, the Neanderthals and Anzick.  Through their DNA, and ours, we reach back tens of thousands of years on the human migration path.  Their journey is also our journey.  It’s absolutely amazing and it’s no wonder people have so many questions and such a sense of enchantment.  But it’s true – and only you can determine exactly what this means to you.



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One Chromosome, Two Sides, No Zipper – ICW and the Matrix

ZipperThe questions I’ve received most often since the release of the new Family Finder Matrix from Family Tree DNA has to do with matches.  Specifically, what the “In Common With” feature is telling you versus what the Family Finder “Matrix” is telling you and how to utilize all of this information together.  At the bottom of this confusion is often a fundamental lack of understanding of how matching occurs and what it means in different contexts.

Let’s talk about this, step by step.

The “in common with” function (called triangulation for a few weeks, but now labeled “run common matches” ) shows you every person that you and one of your matches, match with in common.  I’ll be running this option for my matches with cousin David, shown below.

zipper 1

Here’s an example of my matches in common with my cousin, David.

Zipper 2

The Family Finder Matrix takes this information a bit further and shows you whether or not the people involved with this match, match each other as well.

In this case, I happen to know that my cousins Harold, Carl and Dean will match each other on my father’s side, as will my cousin David.  Warren doesn’t have firm genealogy, but from this, we can tell that he is indeed connected to this family group because he matches me, David, Harold and Carl, but not Dean and not Nova.  We have no idea how Nova connects to this line, if she does.  Notice that Nova does not match any of the other people in this group in the matrix below.  That means that my and David’s common ancestor with her is likely not from this same ancestral line shared by Harold, Carl and Dean.

zipper 3

From this point forward, I would drop back to my trusty downloaded full match spreadsheet that I maintain to see if indeed any of these people match me and my known cousins on the same segments.  If so, that confirms a family/ancestor relationship.   On the snipped from my spreadsheet below, you can see that Warren indeed matches both Buster and David and I, but not on the same segments.  Nova didn’t match any grouping on the same segments.  However, Buster and David both match me on the same portion of chromosome 19, so this confirms that we do share a common ancestor.  In this case, we also know, from our genealogy that the common ancestor is Lazarus Estes and wife, Elizabeth Vannoy.  Based on our multiple cousin matches, we can say that Warren is somehow connected to this line, but we can’t say how.

Zipper 4

I’ve had comments like “I have everything I need on my spreadsheet – I can see where all of my matches match me.”  And indeed, you can, but it’s not everything you need.  Here’s why.

Without additional information, you can’t tell, by just looking at your spreadsheet whether two people who match you on the same segment are matching on your Mom or Dad’s side.  For example, above, I know that both David and Buster are from my Dad’s line, but if I didn’t know that, one of them could be from Mom’s line and one could be from Dad’s, and while they are both related to me, on the same chromosome, they would, in that case, not be related to each other.  So, my spreadsheet of matches tells me clearly THAT people match me, and where, but it doesn’t tell me HOW or on which side.  For that, I need additional tools like ICW, the Matrix and plain old genealogy research.

This is the fundamental concept of matching and in a nutshell, why it’s so difficult.

Every Chromosome Has Two Sides

There are two sides to every chromosome, Mom’s side and Dad’s side.  Except nature has played a cruel trick on us and not installed a zipper.  There are no Mom and Dad labels.  There is no dividing that DNA or those matches in half magically, except by determing who they match, and how they do or don’t match each other.

When we match ourselves against our parents, for example, we then know immediately which half of our DNA came from which parent, but if you don’t have any parents available to match against, then you have to use genealogy or cousin matches to figure that out.

I talk about that in the Chromosome Mapping aka Ancestor Mapping article.

I’m going to use spreadsheets as examples here.  It think they are easier to see and understand, plus, I can manipulate them easily to reflect different situations.

Example 1 – The Very Basics of Matching

At each DNA location, or address, you have two alleles, one from each parent.  These alleles can have one of 4 values, or nucleotides, at each location, represented by the abbreviations T, A, C and G, short for Thymine, Adenine, Cytosine and Guanine.  That’s it, you’re done with all the science words now, so keep reading:)

On any given chromosome, from locations 1-20, you have the following DNA, in our example.

From Mom, you received all As and from Dad, all Cs.  You know that because I’m telling you, but remember, the matching software doesn’t know that because there is no zipper in your DNA.  All the software sees are that you have both an A and an C in location 1 and either an A or C is considered a match.

Zipper 5

In fact, this is what the software sees.  Be aware that in this case, AC=CA.

Zipper 6

Easy so far, right?

Example Two – Mom’s Known Cousin and Dad’s Known Cousin

Now you have two cousins, Mary and Myrtle.  You know, from having known them all of your life and sharing lots of Thanksgiving turkey that they are your family and you know clearly which side of your family they descend from.  Both of your cousins, Mary and Myrtle match you at the same locations on this chromosome, from 5-15.

But Mary is your mother’s cousin, and Myrtle is your Dad’s cousin.  So even though they both match you on the same exact chromosome and the same location, they do not match each other.  Well, let’s put it this way, if they also match each other, then you have an entirely different family genetic genealogy problem, called endogamy, and yes, you might be your own grandpa…but I digress.  But we’re going to assume for this discussion that your mother and father are not related to each other and do not share common ancestors.

Zipper 7

Still easy, right?

Example Three – An Unknown Cousin

Next, we have Martha.  You don’t know Martha, and you don’t know how she is related, but she obviously is.  Martha matches you, but she does not match Myrtle at all, and she doesn’t match Mary on enough overlapping chromosomes to be considered a match to her.  You can see their common match here between Mary and Martha in location 5.  In this case, as it turns out, Martha IS a cousin to Mary on Mom’s side, but we can’t tell that from this information because they don’t match in enough common locations to be above the matching threshold.  With this information, you can’t draw any conclusions.  You will have to wait to see who else Martha matches and look on your spreadsheet to see if Martha matches any of your known cousins and you on common segments which would confirm a common ancestor.  Your download spreadsheet will contain much more detailed information because once you match on any segment above the match threshold of about 7.7cM (plus a few other factors,) all matching segments of 1cM or above are downloaded – so you have a lot of information to work with.

But using both the ICW and matrix tools, Mary might cluster with other cousins on Mom’s side which would provide us with clues as to her relationship.  In fact, the first thing I’d do is to run an ICW with Mary and then utilize the Matrix tool to further define those relationships.

Zipper 8

Still not difficult.

Example Four – A “False Match”

Next we have Jeremy who is also a match to you.

Zipper 9

If you look at how Jeremy matches, you can see that he is actually matching on both sides, Mom’s and Dad’s side, but randomly.  Technically, he is a match to you, because he does match one or the other of your nucleotides at each location, A or C, but without a zipper, we have no idea HOW that DNA is divided in you between Mom and Dad.  In other words, the software doesn’t know that Mom was all A and Dad was all C, unless we’ve phased the data against your parents AND the software knows how to utilize that information.

However, if your parents are one of your matches, you can immediately see which side the match falls on, if either.  In this case, Jeremy doesn’t fall on either side because he is simply a circumstantial match, also known as a match my convergence or a false match.  This is also called IBS, or identical by state, as opposed to IBD, identical by descent.  The smaller the segment you show as a match, especially if there is no clustering, the more likely the match is to be IBS instead of the genealogically desirable IBD.

When people ask how someone can match a child but not a parent, this is the answer.  He matches you on 11 segments, circumstantially, but he only matches your parents on 5 and 6 segments, respectively, which often (but not always) puts him under the matching threshold.  Jeremy may also match Mary, depending on the thresholds.

This is also how someone can match in the “in common with” tool, but not be a match to anyone on the match list in the Matrix.  In fact, this is the power of these multiple tools.

This also doesn’t mean this match is entirely useless, because you DO match.  It may simply not be relevant genealogically.  In “The Autosomal Me” series, I’ve utilized very small match segments that in fact very probably ARE reflective of a common population and not of recent ancestry.  In my Native American research, this is exactly what I was looking for.  You may not be able to utilize this information today, but don’t entirely discount it either.  Just set it aside and move on to a more productive match.

Example Five – Common Matches, Different Ancestors

This situation provides clues, but no proof.

Mary and Joyce both match me on Mom’s segments, but they do not match each other.  They don’t match me on the same segments, so this indicates that they are probably from different ancestors in my Mother’s lines.  As more matches appear, the clusters of people and their genealogy will make this more apparent.

In order to determine which ancestors, I’ll need to work on the genealogy of both Mary and Joyce and see who else they also match on the same segments.  Sometimes the secret of the genealogy match is in the genealogy research or descent of your matches.

Zipper 10

Example Six – Clusters of Cousins

In this example, no one matches Dad, so he’s just out for now.  Susie and Mary match mom on the same segment, which proves that the three of these people share a common ancestor.  Mom and Joyce match each other too, but Joyce doesn’t match Mary and Susie, so they won’t cluster together on the matrix.  However, on the ICW tool, all three women, Joyce, Mary and Susie will match me and Mom.

Using the ICW tool if I were to ICW with Mom, you would see this list:

  • Joyce
  • Mary
  • Susie

The question then becomes, are Joyce, Mary and Susie related to each other, or not.  If so, and to me and Mom, then that indicates a common ancestor within the match group, like me, Joyce and Mom.  The second group doesn’t match the first group – me, Mary, Mom and Susie.  Using these tools together, these people clearly fall into two match groups, the green and blue on the spreadsheet below.  But remember, the match routine doesn’t know which side your As and Cs came from.  All it knows is that you match these people.  But based on these groups and my download spreadsheet common segment matches, I can tell that I’m working with two ancestral lines.

Zipper 11

My matrix for these people would look like this:

Zipper 12

My master matching spreadsheet would now look like this.

zipper 13

When we started, all I would have been able to see is that all of these people matched Mom and Dad and I on the same segments. By utilizing the various tools, I was able to sort into groups and eventually, subgroups.

In fact, you can see below that within Mom’s pink group, there is also the smaller cluster of Mary, Susie, me and Mom.

Zipper 14

For Jeremy and Martha, we can’t do any more right now, so I’ve recorded what we do know and set them aside.

Here, you can see the matches sorted by chromosome, start and end segment.

zipper 16

It looks a lot different than where we started, shown below, when all we had was a list of people who matched each other with no additional information.  We’ve added a lot!

zipper 17

In Summary – Creating the Zipper

So, where are we with this?

By utilizing all of the tools at your disposal, including the ICW tool, the Family Finder Matrix, your matching spreadsheet and your genealogical information, you’re in essence creating that zipper that divides half of your DNA into Mom’s side and Dad’s side.  Then into grandma’s and grandpa’s side, and on up the pedigree chart.

Each of these tools can tell you something unique and important.

The ICW tool tells you who matches you and another person, in common.  It doesn’t tell you if they also match each other.  This tool can provide extremely important clustering information.  For example, if I see unknown cousin Martha clustered with a whole group of known Estes descendants, then that’s a pretty good clue about how I’m related to Martha.  If, on the other hand, I find Martha clustered with people from both sides of my family, well, my Mom and Dad just might be related to each other or their ancestors went to or came from the same places.

By utilizing the Matrix tool, I can tell which of my matches are actually matching each other too, so that puts Martha in a much smaller group, or maybe eliminates her from certain groups.

By then utilizing my downloaded match spreadsheet, on which I record every known tidbit of genealogy information, even generalities like, “family from NC” if that’s the best I can get, I can then see where Martha matches me and others on the same segments, and based on the information in the ICW and the Matrix and my genealogy info, I may be able to slot Martha into a family group.  On a great day – I’ll be able to be more specific and tell her which family group – like we were able to do with my newly found cousin, Loujean.

So, I hope you’ve enjoyed learning how to install a chromosome zipper.  Now you can happily go about unzipping all of that genealogy information held in your DNA, that piece by piece, we’re slowing revealing.

zipper final



I receive a small contribution when you click on some of the links to vendors in my articles. This does NOT increase the price you pay but helps me to keep the lights on and this informational blog free for everyone. Please click on the links in the articles or to the vendors below if you are purchasing products or DNA testing.

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Mitochondrial DNA Convergence and Matches

Every now and then, when I’m doing DNA reports, I run across the perfect example of a DNA phenomenon.  Today, it was a mitochondrial DNA mutation in motion.  Let’s take a look at what happened, how it was discovered and what it means.

mtdna convergence chart

I was contacted a few weeks ago by someone I had been working with on another project.  This woman, we’ll call her June, was concerned because both she and her maternal first cousin, Doris, had both taken mitochondrial DNA tests at Family Tree DNA and they didn’t match each other.  I took a look, of course, and sure enough, at the HVR1 level, there was one mutation difference, at location T16271C.

mtdna convergence

This was particularly interesting, because at the first cousin level, these women shared a maternal grandmother, which means that either June’s mother or Doris’s mother had had a mutation in their mitochondrial DNA, or June or Doris did.  June asked me how she could tell who had the mutation.

I asked if either June or Doris had siblings.  June had a brother, John, so she ordered a kit for John.  If John matched June, then their mother is the one who had the mutation.  If John matched Doris, then June herself had the mutation.

How do I know this, that the mutation didn’t happen in Doris or her mother?  Because the mutation is not “normal” and is listed in the RSRS values in the “extra mutations.”

Furthermore, Doris, who did not carry the extra mutation, had 13,204 matches at the HVR1 level (haplogroup H), where June who did carry the extra mutation only had 41.  Clearly to be useful, genealogically, this test would need to be expanded to the full sequence level.

So June’s brother, John, tested and he matched his sister June, telling us that their mother carried this mutation, and gave it to both of her children.  So the mutation occurred between June’s mother and June’s grandmother.

Are These Matches Valid?

June asked me if her matches were valid.

That’s a tough question to answer, because convergence has occurred.

So let me answer this in two ways.

The matches are technically accurate.  This means that indeed she matches all 41 of the people that the matching routine shows as her exact HVR1 matches.  So in that way, those matches are accurate, but they aren’t valid or meaningful for genealogy.

They aren’t useful, because we know, beyond a doubt that these matches are not related to her in a very long time, probably back into prehistory, because the reason she matches them at the HVR1 level is because she just happened to have the same mutation that all 41 of them carry.  Carrying the same mutation does NOT absolutely mean you share a common ancestor who carried that mutation.  Mutations can occur at any time, and if a mutation happens at this location in the mitochondrial DNA, there is a 1 in 3 chance the person who has the mutation will have the same value as you, since there are only 4 choices, T, A, C, and G, to begin with.  This is what we call convergence, and you’ve just seen it happen.  People match each other, but because they happened to have the same spontaneous mutation, not because they share a common ancestor who had that mutation.  Most of the time, we don’t know whether we are looking at real matches or matches by convergence, but this time, we know for sure, because we can prove that June’s grandmother did not have the mutation, because June’s first cousin, Doris, does not.

So, if June’s HVR1 results aren’t useful to her, whose are?  That’s easy, her cousin Doris’s results are representative of the mitochondrial DNA of their mutual grandmother, so Doris’s matches are actually June and John’s ancestral matches as well.

Could There Be A Fly in the Ointment?

Not matching someone you thought you should match is unsettling.  Could we test someone else to be absolutely positive we’re not dealing with a back mutation?

Certainly, if grandmother had another female child who had children, or if grandmother has a living male child, they can be tested too.  The test on the third child would positively confirm grandmother’s mitochondrial DNA values.

Could we prove positively that the first cousins are actually first cousins, to remove any nagging doubt?

Certainly, using the Family Finder test.



I receive a small contribution when you click on some of the links to vendors in my articles. This does NOT increase the price you pay but helps me to keep the lights on and this informational blog free for everyone. Please click on the links in the articles or to the vendors below if you are purchasing products or DNA testing.

Thank you so much.

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