People, Place, and Time

Telling my family's stories

Tracking ancestors for your X-DNA inheritance

My project the last couple of days has been to fill out and color-code some genealogy charts that pick out my potential X-chromosome ancestors, and X-chromosome ancestors for some of my family members and husband’s family.

Anyone in pink or blue potentially contributed to the DNA in my X chromosomes.

Anyone in pink or blue potentially contributed to the DNA in my X chromosomes (click to enlarge).

My X-ancestors (in pdf format)

These charts are based on the charts Blaine Bettinger posted, and can also be created with some software programs, but since I don’t have one of those programs, I made my own with Reunion and Pages.

If you’re interested in, or already doing, genetic genealogy, then you might want one of these handy-dandy charts too — or maybe a couple of them!  Let’s talk about why.

Who are your X-ancestors?

By X-chromosome ancestors, I mean ancestors that I could inherit my X-chromosomes from.  In my chart above, anyone coloured either pink or blue is an ancestor I could have inherited my X chromosomes from. X chromosomes are one of the sex chromosomes: every woman gets one X from her father and one from her mother; and every man gets one from his mother (he gets a Y chromosome from his father, which is what gets tracked with Y-DNA tests).  In the drawing below, we have a man (square) and woman (circle) with a son and a daughter.  The man passes his blue X chromosome on to his daughter and his green Y chromosome on to his son.

XinheritanceDNA

The woman passes an X chromosome on to both her son and her daughter, and because she has two matched X chromosomes, they can recombine just like the autosomes can.  So every time a woman passes on an  X chromosome to any of her children, it is a potentially different mix of her two X chromosomes, as shown by the different combinations of red and yellow.

A man’s sex chromosomes are mismatched — 1 X and 1 Y — so they can’t recombine.  So whatever X chromosome he inherited from his mother will be passed on intact to all of his daughters, just like the Y chromosome he inherited from his father will be passed on intact to all of his daughters.

So, for me this means I have one X from my father’s mother (because the one he gave me had to have come from her), and one X from my mother.

Implications for inheritance

One of the big variables when you’re thinking about inheritance patterns, is whether you’re male or female.  If you’re male, you will have 1 X chromosome, and it’s going to come from your mother.  This means your X DNA comes from exactly the same ancestors as hers does — and you can use the exact same X-ancestry chart.  Notice in the example below that the entire father’s side of the chart is irrelevant.

A son's X-ancestry

Notice the all of the exact same people are highlighted in these two charts.

Notice the all of the exact same people are highlighted in these two charts.

If you’re female, you’re going to inherit from both your mother and father (again, just like any of the autosomes).  This means you’ll have to create an inheritance chart distinct from your mother’s — and your brother’s!

When you find an “X-match”

If you’ve done autosomal testing with Family Tree DNA or uploaded your DNA results to gedmatch.com, you might find that some of your matches are X-matches.  This means that part of your X chromosome matches part of that other persons X chromosome.  And here’s the important part: in order for you both to inherit this from a common ancestor, that ancestor has to be one of the blue or pink ancestor’s on BOTH YOUR CHART AND YOUR MATCH’S CHART.

This is where having your charts can really, really come in handy, because you can immediately see who to consider and who not to consider — and it really helps narrow the field!

I started making these charts because of exactly one of these scenarios . . . hoping to get to that in the next post! 🙂

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This entry was posted on December 21, 2014 by in Uncategorized and tagged , , , .
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