How to read the X figure on the match list.

+8 votes
127 views
I have just recently added my nephew's dna data to gedmatch.  There is a column for the X-DNA data.  I noted that I have 196.1 cm for his name.  The other few that I found had low amounts of 8.8 and lower.  I was wondering if the high amount for him was because his mother is my sister.  But then why would I have some other very low amounts and what does it mean?
asked Dec 8, 2017 in The Tree House by Janice Anderson G2G4 (4,030 points)
retagged Dec 8, 2017 by Ellen Smith

1 Answer

+6 votes
Hello Janice,

You appear to have the right idea.

If you look at the charts on https://dna-explained.com/2012/09/27/x-marks-the-spot/ you will see that boys can only inherit their X-chromosome from their mother while girls get one from each parent so because your nephew is descended form your sister he gets a lot that is the same as you. If he was descended from your brother he would have zero amount of X in common with you. All those relatives who have any X in common with you are descended from you via grandmothers, ggrandmothers etc

Regards

Graeme
answered Dec 8, 2017 by Graeme Rose G2G5 (5,730 points)
The DNA Ancestors and DNA Descendants features under Family Tree & Tools include a section showing which of your relatives would share X chromosome DNA.

Just a quick comment to make certain folks aren't confused about X-chromosome inheritance: male ancestors are certainly in the picture. A woman gets 50% of her X-chromosome contribution from her father, and (potentially) segments from her maternal grandfather; two of her great-grandfathers; three of her 2g-grandfathers; five of her 3g-grandfathers; eight of her 4g-grandfathers; 13 of her 4g-grandfathers. I say "potentially" because xDNA inheritance doesn't behave at all like we would expect from the per-generation "about 50% rule." Roberta Estes takes a look at this phenomenon in this worthwhile blog post from 2014.

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