Weird X chromosome match.

+11 votes
268 views

I was starting at the top of my DNA matches from GEDmatch and after 30 matches I have matches on 13 of 22 chromosome, so I thought I'd see what the X chromosome looked like.  So I started at the top and the first three were pretty regular, Lots of red, some yellow and a bit of green.  I then got to my known half 3rd cousin once removed and lo and behold except for a tiny bit at the beginning and a even tinier section at the very end, there was no yellow at all.  Most of the chromosome was green with a fair amount of red.  So what's going on?  Our last common ancestor is George Washington Conrad and on my side it goes Female, Male, Female, Male.  On my cousin's side it goes Female, Female, Male Male Male.

So is this an error by GEDmatch, or Ancestry.comDNA or a genetic variation which prevents the Xs from crossing over or chance or what?  His kit ID is A441738

WikiTree profile: George Conrad
in The Tree House by Dave Dardinger G2G6 Pilot (407k points)
retagged by Ellen Smith
Males don't inherit their father's X chromosome.  So your cousin's female, female, male, male, male line could not be a path of X-DNA inheritance.

How many cMs on your X chromosome do you share with A441738?
Actually I worded that badly.  I don't have an X chromosome match with him, just an auDNA match which is in two matches totalling 34.5 cM.
As Peter said, you wouldn't be expected to have an X chromosome match with this male cousin who has three generations of males between himself and this common ancestor. http://www.wikitree.com/treewidget/Conrad-1528/890 shows your ancestor's descendants who would be expected to have his X-chromosome DNA.

1 Answer

+4 votes
It's possible you didn't inherit the same X.  There's a lot of variation in there with the females who get the X from both sides.  Males only get it from one side (mom), but mom got it from two sides...so she could pass on either one.  You and your cousin may have gotten completely different ones.
by Summer Orman G2G6 Mach 8 (86.2k points)
For instance, me and my 2 cousins (different sides) share absolutely NO X chromosome at all.

Me: A239508, them: M412011, T334244
Having looked at a larger sample of the Xs I have 10 with all three colors, 8 of green and red and 2 yellow and red.  All of the two colors have a smallish section of all three at the beginning and a tiny section at the end.  Though a couple of the greenie ones have essentially no yellow at all.  I guess I need to look at how X chromosomes work.

Dave, if you set the Gedmatch X comparison values 

  • "SNP count minimum " to 100
  • "Minimum segment cM size" to 1

You will see some blue below the chart. For this purpose, Blue is really all we are concerned with.  The numbers I choose are too low to be of any value.  I only choose them so you could see an example of blue with the same match.

I believe FTDNA uses 500 and 5, and 23andme uses 200 and 1 when you are comparing males to males.

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