Y DNA: Part 2 – The Dictionary of DNA

After my introductory article, Y DNA: Part 1 – Overview, I received several questions about terminology, so this second article will be a dictionary or maybe more like a wiki. Many terms about Y DNA apply to mitochondrial and autosomal as well.

Haplogroup – think of your Y or mitochondrial DNA haplogroup as your genetic clan. Haplogroups are assigned based on SNPs, specific nucleotide mutations that change very occasionally. We don’t know exactly how often, but the general schools of thought are that a new SNP mutation on the Y chromosome occurs someplace between every 80 and 145 years. Of course, those would only be averages. I’ve as many as two mutations in a father son pair, and no mutations for many generations.

Dictionary haplogroup.png

Y DNA haplogroups are quite reliably predicted by STR results at Family Tree DNA, meaning the results of a 12, 25, 37, 67 or 111 marker tests. Haplogroups are only confirmed or expanded from the estimate by SNP testing of the Y chromosome. Predictions are almost always accurate, but only apply to the upper level base haplogroups. I wrote about that in the article, Haplogroups and the Three Brothers.

Haplogroups are also estimated by some companies, specifically 23andMe and LivingDNA who provide autosomal testing. These companies estimate Y and mitochondrial haplogroups by targeting certain haplogroup defining locations in your DNA, both Y and mitochondrial. That doesn’t mean they are actually obtaining Y and mtDNA information from autosomal DNA, just that the chip they are using for DNA processing targets a few Y and mitochondrial locations to be read.

Again, the only way to confirm or expand that haplogroup is to test either your Y or mitochondrial DNA directly. I wrote about that in the article Haplogroup Comparisons Between Family Tree DNA and 23andMe and Why Different Haplogroup Results?.

Nucleotide – DNA is comprised of 4 base nucleotides, abbreviated as T (Thymine), A (Adenine), C (Cytosine) and G (Guanine.) Every DNA address holds one nucleotide.

In the DNA double helix, generally, A pairs with T and C pairs with G.

Dictionary helix structure.png

Looking at this double helix twist, green and purple “ladder rungs” represent the 4 nucleotides. Purple and green and have been assigned to one bonding pair, either A/T or C/G, and red and blue have been assigned to the other pair.

When mutations occur, most often A or T are replaced with their paired nucleotide, as are C and G. In this example, A would be replaced with T and vice versa. C with G and vice versa.

Sometimes that’s not the case and a mutation occurs that pairs A with C or G, for example.

For Y DNA SNPs, we care THAT the mutation occurred, and the identity of the replacing nucleotide so we know if two men match on that SNP. These mutations are what make DNA in general, and Y DNA in particular useful for genealogy.

The rest of this nucleotide information is not something you really need to know, unless of course you’re playing in the jeopardy championship. (Yes, seriously.) The testing lab worries about these things, as well as matching/not matching, so you don’t need to.

SNP – Single nucleotide polymorphism, pronounced “snip.” A mutation that occurs when the nucleotide typically found at a particular location (the ancestral value) is replaced with one of the other three nucleotides (the derived value.) SNPs that mutate are called variants.

In Y DNA, after discovery and confirmation that the SNP mutation is valid and carried by more than one man, the mutation is given a name something like R-M269 where R is the base haplogroup and M269 reflects the lab that discovered and named the SNP (M = Peter Underhill at Stanford) and an additional number, generally the next incremental number named by that lab (269).

Some SNPs were discovered simultaneously by different labs. When that happens, the same mutation in the identical location is given different names by different organizations, resulting in multiple names for the name mutation in the same DNA location. These are considered equivalent SNPs because they are identical.

In some cases, SNPs in different locations seem to define the same tree branching structure. These are functionally equivalent until enough tests are taken to determine a new branching structure, but they are not equivalent in the sense that the exact same DNA location was named by two different labs.

Some confusion exists about Y DNA SNP equivalence.

Equivalence Confusion How This Happens Are They the Same?
Same exact DNA location named by two labs Different SNP names for the same DNA location, named by two different labs at about the same time Exactly equivalent because SNPs are named for the the exact same DNA locations, define only one tree branch ever
Different DNA locations and SNP names, one current tree branch Different SNPs temporarily located on same branch of  the tree because branches or branching structure have not yet been defined When enough men test, different branches will likely be sorted out for the non-equivalent SNPs pointing to newly defined branch locations that divide the tree or branch

Let’s look at an example where 4 example SNPs have been named. Two at the same location, and two more for two additional locations. However, initially, we don’t know how this tree actually looks, meaning what is the base/trunk and what are branches, so we need more tests to identify the actual structure.

Dictionary SNPs before branching.png

The example structure of a haplogroup R branch, above, shows that there are three actual SNP locations that have been named. Location 1 has been given two different SNP names, but they are the same exact location. Duplicate names are not intentionally given, but result from multiple labs making simultaneous discoveries.

However, because we don’t have enough information yet, meaning not enough men have tested that carry at least some of the mutations (variants,), we can’t yet define trunks and branches. Until we do, all 4 SNPs will be grouped together. Examples 1 and 2 will always be equivalent because they are simply different names for the exact same DNA location. Eventually, a branching structure will emerge for Examples 1/2, Example 3 and Example 4..

Dictionary SNP branches.png

Eventually, the downstream branches will be defined and split off. It’s also possible that Example 4 would be the trunk with Examples 1 and 2 forming a branch and Example 3 forming a branch. Branching tree structure can’t be built without sufficient testers who take the NGS tests, specifically the Big Y-700 which doesn’t just confirm a subset of existing named SNPs, but confirms all named SNPs, unnamed variants and discovers new previously-undiscovered variants which define the branching tree structure.

SNP testing occurs in multiple ways, including:

  • NGS, next generation sequencing, tests such as the Big Y-700 which scans the gold standard region of the Y chromosome in order to find known SNPs at specific locations, mutations (variants) not yet named as SNPs, previously undiscovered variants and minimally 700 STR mutations.
  • WGS, whole genome sequencing although there currently exist no bundled commercial tools to separate Y DNA information from the rest of the genome, nor any comparison methodology that allows whole genome information to be transferred to Family Tree DNA, the only commercial lab that does both testing and matching of NGS Y DNA tests and where most of the Y DNA tests reside. There can also be quality issues with whole genome sequencing if the genome is not scanned a similar number of times as the NGS Y tests. The criteria for what constitues a “positive call” for a mutation at a specific location varies as well, with little standardization within the industry.
  • Targeted SNP testing of a specific SNP location. Available at Family Tree DNA  and other labs for some SNP locations, this test would only be done if you are looking for something very specific and know what you are doing. In some cases, a tester will purchase one SNP to verify that they are in a particular lineage, but there is no benefit such as matching. Furthermore, matching on one SNP alone does not confirm a specific lineage. Not all SNPs are individually available for purchase. In fact, as more SNPs are discovered at an astronomical rate, most aren’t available to purchase separately.
  • SNP panels which test a series of SNPs within a certain haplogroup in order to determine if a tester belongs to a specific subclade. These tests only test known SNPs and aren’t tests of discovery, scanning the useable portion of the Y chromosome. In other words, you will discern whether you are or are not a member of the specific subclades being tested for, but you will not learn anything more such as matching to a different subclade, or new, undiscovered variants (mutations) or subclades.

Subclade – A branch of a specific upstream branch of the haplotree.

Dictionary R.png

For example, in haplogroup R, R1 and R2 are subclades of haplogroup R. The graphic above conveys the concept of a subclade. Haplogroups beneath R1 and R2, respectively, are also subclades of haplogroup R as well as subclades of all clades above them on the haplotree.

Older naming conventions used letter number conventions such as R1 and R2 which expanded to R1b1c and so forth, alternating letters and numbers.

Today, we see most haplogroups designated by the haplogroup letter and SNP name. Using that notation methodology, R would be R-M207, R1 would be R-M173 and R2 would be R-M479.

Dictionary R branches.png

ISOGG documents Y haplogroup naming conventions and their history, maintaining both an alphanumeric and SNP tree for backwards compatibility. The reason that the alphanumeric tree was obsoleted was because there was no way to split a haplogroup like R1b1c when a new branch appeared between R1b and R1b1 without renaming everything downstream of R1b, causing constant reshuffling and renaming of tree branches. Haplogroup names were becoming in excess of 20 characters long. Today, the terminal SNP is used as a person’s haplogroup designation. The SNP name never changes and the individual’s Y haplogroup only changes if:

  • Further testing is performed and the tester is discovered to have an additional mutation further downstream from their current terminal SNP
  • A SNP previously discovered using the Big Y NGS test has since been named because enough men were subsequently discovered to carry that mutation, and the newly named SNP is the tester’s terminal SNP

Terminal SNP – It’s really not fatal. Used in this context, “terminal” means end of line, meaning furthest down and closest to present in the haplotree.

Depending on what level of testing you’ve undergone, you may have different haplogroups, or SNPs, assigned as your official “end of line” haplogroup or “terminal SNP” at various times.

If you took any of the various STR panel tests (12, 25, 37, 67 or 111) at Family Tree DNA your SNP was predicted based on STR matches to other men. Let’s say that prediction is R-M198. At that time, R-M198 was your terminal SNP. If you took the Big Y-700 test, your terminal SNP would almost assuredly change to something much further downstream in the haplotree.

If you took an autosomal test, your haplogroup was predicted based on a panel of SNPs selected to be informative about Y or mitochondrial DNA haplogroups. As with predicted haplogroups from STR test panels, the only way to discover a more definitive haplogroup is with further testing.

If you took a Y DNA STR test, you can see by looking at your match list that other testers may have a variety of “terminal SNPs.”

Dictionary Y matches.png

In the above example, the tester was originally predicted as R-M198 but subsequently took a Big Y test. His haplogroup now is R-YP729, a subclade of R-M198 several branches downstream.

Looking at his Y DNA STR matches to view the haplogroups of his matches, we see that the Y DNA predicted or confirmed haplogroup is displayed in the Y-DNA Haplogroup column – and several other men are M198 as well.

Anyone who has taken any type of confirming SNP test, whether it’s an individual SNP test, a panel test or the Big Y has their confirmed haplogroup at that level of testing listed in the Terminal SNP column. What we don’t know and can’t tell is whether the men whose Terminal SNP is listed as R-M198 just tested that SNP or have undergone additional SNP testing downstream and tested negative for other downstream SNPs. We can tell if they have taken the Big Y test by looking at their tests taken, shown by the red arrows above.

If the haplogroup has been confirmed by any form of SNP testing, then the confirmed haplogroup is displayed under the column, “Terminal SNP.” Unfortunately, none of this testers’ matches at this STR marker level have taken the Big Y test. As expected, no one matches him on his Terminal SNP, meaning his SNP farthest down on the tree. To obtain that level of resolution, one would have to take the Big Y test and his matches have not.

Dictionary Y block tree.png

Looking at this tester’s Big Y Block Tree results, we can see that there are indeed 3 people that match him on his terminal SNP, but none of them match him on the STR tests which generally produce genealogical matches closer in time. This suggests that these haplogroup level matches are a result of an ancestor further back in time. Note that these men also have an average of 5 variants each that are currently unnamed. These may eventually be named and become baby branches.

SNP matches can be useful genealogically, depending on when they occurred, or can originate further back in time, perhaps before the advent of surnames.

Our tester’s paternal ancestors migrated from Germany to Hungary in the late 1700s or 1800s, settling in a region now in Croatia, but he’s brick-walled on his paternal line due to record loss during the various wars.

The block tree reveals that the tester’s Big Y SNP match is indeed from Germany, born in 1718, with other men carrying this same terminal SNP originating in both Hungary and Germany even though they aren’t shown as a STR marker match to our tester.

You can read more about the block tree in the article, Family Tree DNA’s New Big Y Block Tree.

Haplotype – your individual values for results of gene sequencing, such as SNPs or STR values tested in the 12, 25, 37, 67 and 111 marker panels at Family Tree DNA. The haplotype for the individual shown below would be 13 for location DYS393, 26 for location DYS390, 16 for location DYS19, and so forth.

Dictionary panel 1.png

The values in a haplotype tend to be inherited together, so they are “unique” to you and your family. In this case, the Y DNA STR values of 13, 26, 16 and 10 are generally inherited together (unless a new mutation occurs,) passed from father to son on the Y chromosome. Therefore, this person’s haplotype is 13, 26, 16 and 10 for these 4 markers.

If this haplotype is rare, it may be very unique to the family. If the haplotype is common, it may only be unique to a much larger haplogroup reaching back hundreds or thousands of years. The larger the haplotype, the more unique it tends to be.

STR – Short tandem repeat. I think of a short tandem repeat as a copy machine or a stutter error. On the Y chromosome, the value of 13 at the location DYS393 above indicates that a series of DNA nucleotides is repeated a total of 13 times.

Indel example 1

Starting with the above example, let’s see how STR values accrue mutations.

STR example

In the example above, the value of CT was repeated 4 times in this DNA sequence, for a total of 5, so 5 would be the marker value.

Indel example 3

DNA can have deletions where the DNA at one or more locations is deleted and no DNA is found at that location, like the missing A above.

DNA can also have insertions where a particular value is inserted one or more times.

Dictionary insertion example.png

For example, if we know to expect the above values at DNA locations 1-10, and an insertion occurs between location 3 and 4, we know that insertion occurred because the alignment of the pattern of values expected in locations 4-10 is off by 1, and an unexpected T is found between 3 and 4, which I’ve labeled 3.1.

Dictionary insertion example 1.png

STR, or copy mutations are different from insertions, deletions or SNP mutations, shown below, where one SNP value is actually changed to another nucleotide.

Indel example 2

Haplotree – the SNP trees of humanity. Just a few years ago, we thought that there were only a few branches on the Y and mitochondrial trees of humanity, but the Big Y test has been a game changer for Y DNA.

At the end of 2019, the tree originating in Africa with Y chromosome Adam whose descendants populated the earth is comprised of more than 217,277 variants divided into 24,838 individual Y haplotree branches

A tree this size is very difficult to visualize, but you can take a look at Family Tree DNA’s public Y DNA tree here, beginning with haplogroup A. Today, there 25,880 branches, increased by more than 1000 branches in less than 3 weeks since year end. This tree is growing at breakneck speed as more men take the Big Y-700 test and new SNPs are discovered.

On the Public Y Tree below, as you expand each haplogroup into subgroups, you’ll see the flags representing the locations of where the testers’ most distant paternal ancestor lived.

Dictionary public tree.png

I wrote about how to use the Y tree in the article Family Tree DNA’s PUBLIC Y DNA Haplotree.

The mitochondrial tree can be viewed here. I wrote about to use the mitochondrial tree in the article Family Tree DNA’s Mitochondrial Haplotree.

Need Something Else?

I’ll be introducing more concepts and terms in future articles on the various Y DNA features. In the mean time, be sure to use the search box located in the upper right-hand corner of the blog to search for any term.

DNAexplain search box.png

For example, want to know what Genetic Distance means for either Y or mitochondrial DNA? Just type “genetic distance” into the search box, minus the quote marks, and press enter.

Enjoy and stay tuned for Part 3 in the Y DNA series, coming soon.

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Glossary – Terminal SNP

What is a Terminal SNP?

It sounds fatal doesn’t it, but don’t worry, it’s not.

The phrase Terminal SNP is generally used in conjunction with discussing Y DNA testing and haplogroup identification.

SNPs Define Haplogroups

In a nutshell, SNPs, single nucleotide polymorphisms, are the mutations that define different haplogroups. Haplogroups reach far back in time on the direct paternal, generally the surname, line.

SNPs, mutations that define haplogroups are considered to be “once in the lifetime of mankind” events that divide one haplogroup into two subgroups, or branches.

A haplogroup can be thought of as the ancient genetic clan of males – specifically their Y DNA. You might want to read the article, What is a Haplogroup?

If you test your Y DNA with Family Tree DNA, you’ll notice that you receive an estimated haplogroup with the regular Y DNA tests which test STR, or short tandem repeat, markers. STRs are the markers tested in the 37, 67 or 111 marker tests. You can read about the difference between STRs and SNPs in the article, STRs vs SNPs, Multiple DNA Personalities.

STR markers are used for more recent genealogical testing and comparison, while haplogroups reach further back in time.

An estimated haplogroup as provided by Family Tree DNA is based on STR matches to people who have done SNP testing. Estimated haplogroups are quite accurate, as far as they go. However, by necessity, they aren’t deep haplogroups, meaning they aren’t the leaves on the end of the twigs of the branch of your haplotree. Estimated haplogroups are the big branches.

In essence, what a haplogroup provided with STR testing tells you is the name of the town and the main street through town. To get to your house, you may need to turn on a few side streets.

Haplotree

The haplotree, back in the ancient days of 2002 used to hold less than 100 haplogroups, each main branch called by a different letter of the alphabet. The main branches or what is referred to as the core backbone is shown in this graphic from Wikipedia.

Today, the haplotree shown for each Y DNA tester on their personal page at Family Tree DNA, has tens of thousands of branches. No, that’s not a misprint.

The haplotree is the phylogenetic tree that defines all of the branches of mankind and groups them into increasingly refined “clans” or groups, the further down the tree you go.

In other words, Y Adam is at the root, then his “sons” who, due to specific mutations, formed different base haplogroups. As more mutations occurred in the son’s descendants’ lines, more haplogroups were born. Multiply that over tens of thousands of years, and you have lots of branches and twigs and even leaves on the branches of this tree of humanity.

Let’s look at the terminal SNP of my cousin, John, on his Haplotree and SNP page at Family Tree DNA.

John’s terminal SNP is R-BY490. R indicates the main branch and BY490 is the name of the SNP that is the further down the tree – his leaf, for lack of a better definition.

In John’s case, we know this is the smallest leaf on his branch, because he took the Big Y test which reads all of his SNPs on the Y chromosome.

Haplogroup R is quite large with thousands of branches and leaves – each one with its own distinct history that is an important part of your genealogy. Tracking where and when these mutations happened tells you the migration history of your paternal ancestor.

How else would you ever know?

How Do I Discover My Terminal SNP?

Sometimes “terminal SNP” is used to mean the SNP for which a man has most recently tested. It may NOT mean that he has tested for all of the available SNPs. What this really means is that when someone gives you a terminal SNP name, or you see one listed someplace, you’ll need to ask about the depth of the testing undergone by the man in question.

Let’s look at an example.

I’ve condensed John’s tree into only the SNPs for which he tested positive. The entire tree includes SNPs that John tested negative for, and their branches which are not relevant to John – although we certainly didn’t know that they weren’t relevant before he tested. However, he may want to reference the large and accurate scientific tree, so all information is provided to John. It’s like seeing a map that includes all roads, not just the one you’re traveling.

I’ve created a descendant chart style tree below. Y line Adam is the first male. Some several thousands of years later, his descendant had a mutation that created haplogroup R defined by the SNP M207, in yellow.

John, based on his STR matches, was predicted to be R-M269. On his results page, that’s the estimated haplogroup that was showing when his results were first returned.

If you had asked John about his terminal SNP, he would have probably told you R-M269. At that time, to the best of his knowledge, that WAS his terminal SNP – but it wasn’t really.

John could choose three ways to test for additional SNPs to discover his actual terminal SNP.

  • One by One

John could selectively test one SNP at a time to see if he was positive, meaning that he has that mutation. SNPs cost $39 each to test, as of the time this article was written. Of course, John could also be negative for that SNP, meaning he doesn’t have the SNP, and therefore does not descend from that line. That’s good information too, but then John would have to select another branch to test by purchasing the SNP associated with that new branch.

If John had selected any of the SNPs on the list above to test, he would have tested positive. So, let’s say John decided to test L21, a major branch. If he tested positive, that means that all of the branches directly above L21, between L21 and M207, are also positive, by inference.

At that point, John would tell you that his terminal SNP is L21, but it isn’t actually.

  • SNP Packs

Now, John wants to purchase a more cost-effective SNP pack, because he can test 100 or more SNP locations by purchasing one SNP pack for $99. That’s a great value, so John purchases the SNP pack offered on his personal page. A SNP pack tests selective SNPs all over the relevant portion of the tree in an attempt to place a man on a relatively low branch. These SNPs are selected to find an appropriate branch, not the appropriate leaf. They confirm (or disprove) SNPs that have already been discovered.

Let’s say, in John’s case, the SNP pack moves him down to R-ZP21. If you asked him now about his terminal SNP, he would probably tell you R-ZP21, but it still isn’t actually.

SNP packs are great and do move people down the tree, but the only way to move to the end of the twigs is the Big Y test.

  • The Big Y Test

The Big Y test tests for all known SNPs as well as what were called Novel Variants and are now called Unnamed Variants which are new SNPs discovered that are as yet unnamed. You may have a new SNP in your line waiting to be discovered. The Estes family has one dating from sometime before 1495 that, to date, has only been found in Estes descendant males from that common ancestor who was born in 1495.

The Big Y test scans virtually the entire Y chromosome in order to place testers on the lowest leaf of the tree. You can’t get there any other way with certainty and you’ll never know if you have any as yet undiscovered SNPs or leaves unless you take the Big Y.

In John’s case, that leaf was 4 more branches below R-ZP21, at R-BY490.

Why Does a Terminal SNP Matter?

Haplogroup R-M269 is the most common haplogroup of European men.

Looking at the SNP map, you can see that there are so many map locations as to color the map of the UK entirely red.

Genealogically, this isn’t helpful at all.

However, looking now at DF49, below, we see many fewer locations, suggesting perhaps that men with this terminal SNP are clustered in particular areas.

SNPS further down John’s personal haplotree tell an increasingly focused and granular story, each step moving closer in time.

Summary

Men generally want to discover their terminal SNP with the hope that they can learn something interesting about the migration of their ancestors before the genesis of surnames.

Perhaps they will discover that they match all men with McSurnames, suggesting perhaps a Scottish origin. Or maybe their terminal SNP is only found in a mountainous region of Germany, or perhaps their Big Y matches all have patronymic surnames from Scandinavia.

Big Y testing is also a community sourced citizen science effort to expand the Y haplotree – and quite successfully. The vast majority of SNPs on the publicly available ISOGG Y tree today are from individual testers, not from academic studies.

Haplogroups, and therefore terminal SNPs are the only way we have to peek back behind the veil of time.

If you’re interested in discovering your terminal SNP, you’ll be money ahead to simply purchase the Big Y up front and skip individual SNP testing along with SNP packs. In addition to discovering your terminal SNP, you are also matched to other men who have taken the Big Y test.

You can order the Big Y, individual SNPs or SNP packs by clicking on this link, signing on to your account, and then clicking on the blue “Upgrade” button, either in the Y DNA section, shown below, or in the upper right hand corner of your personal page.

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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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Glossary – DNA – Deoxyribonucleic Acid

What is DNA and why do I care?

Good questions. Let’s take a look at the answer in general, then why we use DNA for genealogy.

The Recipe for You

DNA, deoxyribonucleic acid, is the book of life for all organisms. In essence, it’s the recipe for you – and what makes you unique.

DNA is formed of strands that twist to form the familiar double helix pattern.

The two strands are joined together by one of 4 different nucleotides, one extending from each side to connect in the middle. The nucleotides are:

  • Cytosine – C
  • Guanine – G
  • Thymine – T
  • Adenine – A

The nucleotide names don’t really matter for genetic genealogy, but what does matter is that the sequence of these nucleotides when chained together is what encodes information on long structures called chromosomes. Each person carries 22 chromosomes, plus the 23rd chromosome pair which is gender specific.

Using DNA for Genetic Genealogy

There are four different kinds of DNA that genealogists use in different ways for obtaining ancestors’ information relevant to genetic genealogy. Thankfully, we have 4 different kinds of DNA available to us because of unique inheritance patterns for each kind of DNA – meaning we inherited different kinds of DNA from different ancestral paths. If one kind of DNA doesn’t work in a particular situation, chances are good that another type will.

Genetic genealogy makes use of 4 different types of DNA.

  • Y DNA – passed from males to male children, only (your father’s paternal line)
  • Mitochondrial DNA – passed from females to both genders of children, but only females pass it on (your mother’s matrilineal line)

Y and mitochondrial DNA inheritance paths are shown on a pedigree chart in the graphic below, with the blue boxes representing Y DNA and the red circles representing mitochondrial DNA inheritance.

In addition to Y and mitochondrial DNA, genetic genealogists also use two kinds of DNA that reflect inheritance from additional ancestral lines, in addition to the red and blue lines shown above – meaning the ancestral lines with no color.

  • Autosomal DNA – the 22 chromosomes that recombine during reproduction.
  • X Chromosome – always contributed by the mother, but only contributed by the father to female children – this is the 23rd chromosome pair which recombines with a unique inheritance pattern.  You can read more about that in the article, X Marks the Spot.

Receiving What Kind of DNA from Whom

While the Y and mitochondrial DNA have unique and very prescribed inheritance patterns as shown by the red arrows pointing to the blue Y chromosome below at far left, and the red mitochondrial circles at far right, the 22 autosomal chromosomes are contributed equally by each parent. In other words, for each chromosome, a child inherits half of each parent’s DNA. How the selection of which DNA is contributed to each child is unknown.

A child’s gender is determined by the parent’s contributions to the 23rd chromosome, not shown above. The following chart explains gender determination by the X and Y combinations of the 23rd chromosome.

Received from Mother Received from Father
Male child X Y
Female child X X

The Y chromosome is what makes males male.

No Y chromosome?  You’re a female.

However, this X chromosome inheritance pattern provides us with the ability to look at X matches for males and know immediately that they had to have come from his mother’s lineage – because males don’t inherit an X chromosome from their father.

Autosomal DNA and Genetic Genealogy

The 22 non-gender chromosomes recombine in each generation, with half of each chromosome being contributed by each parent, as shown in the illustrations above.

You can see that in the first generation, the child received one blue and one yellow, or one pink and one green, chromosome. In giving each child exactly half of their DNA, each parent contributes some amount of ancestral DNA from generations upstream, as you can see in the mother/father and son/daughter generations.

For example, each child receives, on average, 25% of each of their grandparent’s DNA – although they can receive somewhat more or less than 25%, depending on the random nature of recombination.

Therefore, genetic genealogy testing companies compare tester’s autosomal DNA with other testers and look for common segments contributed by common ancestors, resulting in autosomal matching.

When relatively large segments match between three or more relatives who are not immediate family, we can attribute that DNA to a common ancestor. Of course, the challenge, and the thrill, is to determine which common ancestor contributed that common DNA to our triangulated match group. It’s a great way to verify our research and to break down brick walls.

Let’s face it, you received ALL of your DNA from SOME combination of ancestors, and if you carry large enough pieces from any specific ancestor, we can, hopefully, identify the source of that DNA segment by looking at the genealogy of those we match on that segment.

It’s a great puzzle to unravel, and best of all, it’s the puzzle of you.

More Info

The great news is that you can utilize your Y DNA, mitochondrial DNA and autosomal DNA differently, to provide you with different kinds of information about different ancestors and genealogy lines.

If you’d like to read more about how the 4 Kinds of DNA can be used, please read the short article, 4 Kinds of DNA for Genetic Genealogy.

You can also enter any word or phrase into the search box in the upper right hand corner of this blog to find additional useful information about any topic.

If You Want to Test

If you’d like to learn more about the various kinds of DNA tests available, and which one or ones would be the best for you, please read the article, Which DNA Test is Best?

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Disclosure

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.

DNA Purchases and Free Transfers

Genealogy Services

Genealogy Research