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Identifying Possible Common Ancestors Utilizing Multiple Tests

Roberta Estes

There is a significant amount of confusion about DNA matching and which ancestors and ancestral lines can match in which way.

To review, there are 4 different kinds of DNA that we can utilize for genealogy, the Y DNA for males, mitochondrial, X chromosome and autosomal DNA for both males and females.  You can read an intro article about how these different types of DNA are utilized here.

Clearly, the mitochondrial DNA addresses only one line – your mother’s matrilineal line, shown in red below – and the mitochondrial DNA is never divided or mixed with that of the father.  So you share the mitochondrial DNA with thousands of generations of your matrilineal ancestors.  You’ve accumulated a few mutations over those generations, which serve to show us who you are most closely related to.

The Y chromosome is passed only from father to son, shown in blue above.

If you haven’t read this article I wrote about X matching, please do.  Males and females have a different inheritance path for the X chromosome because males don’t inherit an X from their father’s, but females do.

Even better, if you utilize software that can interface with Progeny Software’s Charting Companion, by all means, purchase this add-on program because it shows you on your own tree which of your ancestors X chromosome you have the potential of carrying.  I wrote about how to utilize this great tool here.

The X chromosome acts like autosomal DNA, the DNA we receive from all of our ancestral lines, including red and blue lines above, and all of the blank ones in-between, meaning that the X chromosome is a candidate to be recombined and divided in each generation.  I say a candidate, because sometimes the X is passed in very large pieces. Not quite what or how we might expect.  I wrote about that here.

But we can’t and don’t know whose X we carry, or which pieces of which ancestors’ Xs we carry – but we do know, based on how DNA is passed generation to generation, whose X DNA we MIGHT carry – and whose we cannot carry.

Because women inherit an X from both parents, and men only inherit the X from their mother, the inheritance pattern through the generations is different for males and females, so each person needs to plot out their potential X ancestors.

A female could carry some part of the X chromosome of any of the ancestors whose names would fall into the pink or blue boxes of this fan chart.  You can NOT inherit any X from someone whose box is blank (no color).

These blank charts are courtesy of Blaine Bettinger.  He originally published them on his blog, The Genetic Genealogist, in December 2008 and January 2009 in his articles about how to use the X chromosome for genealogy.

A male’s fan chart for the X chromosome looks a bit different because the male doesn’t inherit an X from his father.  Instead, he inherits the Y chromosome which makes him a male.

So let’s see if we can approach this combination of information and DNA test types in a bit of a different way.  A female can inherit the following kinds of DNA from the ancestors listed at the left in the chart below.  This chart compiles information from all of the 4 different types of DNA that we can use for genealogical purposes. Generation number is in parenthesis.

Female’s Ancestor Inheritance Chart

Here’s how to read this chart.

Does a female inherit Y DNA from her mother?  No

Does a female inherit mtDNA from her mother?  Yes

Does a female inherit the X chromosome from her mother?  Yes

Does a female inherit autosomal DNA from her mother?  Yes

­Ancestor Y DNA mtDNA X Chr Autosomal
Mother (1) No – she doesn’t have one Yes Yes Yes
Father (1) No – you’re a female No – only passed from mother Yes Yes
Mother’s mother (2) No Yes Yes Yes
Mother’s father (2) No No Yes Yes
Father’s father (2) No No No – your father didn’t get an X from his father Yes
Father’s mother (2) No No – father’s don’t contribute mtDNA to children Yes Yes
Mother’s mother’s mother (3) No Yes Yes Yes
Mother’s mother’s father (3) No No Yes Yes
Mother’ father’s mother (3) No No Yes Yes
Mother’s father’sFather (3) No No No Yes
Father’s father’s father (3) No No No Yes
Father’s father’s mother (3) No No No Yes
Father’s mother’s mother (3) No No Yes Yes
Father’s mother’s father (3) No No Yes Yes

You can personalize this chart by inserting your own ancestor’s names and complete additional generations by:

This same chart for a male would look somewhat different, but only in the X and Y columns.

Males’ Ancestor Inheritance Chart

Ancestor Y DNA mtDNA X Chr Autosomal
Mother (1) No – she doesn’t have one Yes Yes Yes
Father (1) Yes, you received your father’s No – only passed from mother No – You received the Y instead Yes
Mother’s mother (2) No Yes Yes Yes
Mother’s father (2) No No Yes Yes
Father’s father (2) Yes, your father received his Y No No – your father didn’t get an X from his father Yes
Father’s mother (2) No No – father’s don’t contribute mtDNA to children No – you received no X from your father Yes
Mother’s mother’s mother (3) No Yes Yes Yes
Mother’s mother’s father (3) No No Yes Yes
Mother’ father’s mother (3) No No Yes Yes
Mother’s father’sFather (3) No No No Yes
Father’s father’s father (3) Yes No No Yes
Father’s father’s mother (3) No No No Yes
Father’s mother’s mother (3) No No No Yes
Father’s mother’s father (3) No No No Yes

So, how could this help you with your genealogy?  Let’s say that you match someone on the X chromosome, but you know that you are not a mitochondrial match.  You can look on this chart and eliminate any line that includes a mtDNA match.  You know your X match is not from that line.  You can also eliminate any ancestral line that does not include a potential X match.  The ancestors you are left with are your possible match ancestors.

Let’s use the female chart below as an example.  The greyed out ancestors are those removed by virtue of no mitochondrial DNA match, so anyone with a Yes in that box.  It also eliminates anyone who could not contribute an X chromosome, so with a No in that box.  Any greyed out box eliminated that specific ancestor from consideration.

Please note that by eliminating your mother, it does not eliminate her entire line.  It only means, in this case, that if your mitochondrial DNA doesn’t match, then you and your match don’t share a common mother.  Your mother’s father is still a possibility.  And you can still match on just the X but not through the dual mito line.

Female Example of X Match Ancestor Elimination

Therefore, only the ancestors left unshaded are candidates for matches.

Male Example of Ancestor Elimination

Of course, on a male’s chart, the X becomes much more restricted due to the fact that men inherit the Y chromosome and not the X from their fathers.  You’ll notice that if a specific ancestor carries a matching Y chromosome, they cannot carry the matching X – they are mutually exclusive.

As you can see, by the time we’re done eliminating possibilities, there are only three possible ancestral lines to pursue for the X match who doesn’t match on the Y or the mitochondrial DNA.

Conversely, if you have someone who matches on the X AND on a mitochondrial line, that is a huge hint and that line would be the first one I would pursue.

You can expand this chart to any number of generations.  I stopped at 3 for illustration purposes.

While this methodology doesn’t exactly tell you who your common X matching ancestor is, it certainly narrows the playing field substantially.  Finding an X chromosome match can be a real bonus, especially when combined with other types of DNA testing.

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