X Chromosome matches on Gedmatch.com

General discussions regarding the X-Chromosome.

Posts: 1
Joined: Fri Mar 30, 2012 2:12 pm

MtDNA:
U2e1a1
PostPosted: Wed Sep 19, 2012 3:09 pm
I am trying to learn more about X-Chromosome matches and what you can learn from them.

There are 7 of us who match on high resolution mtDNA (HVR2) match at FTDNA. Two others are in the US and 4 are in Finland.

One of the two others in the US and I found that we share a common maternal third great grandmother. We do not match each other on autosomal either at FTDNA or Gedmatch.com, but we do have a considerable X Chromosome match at Gedmatch.com.

I am trying to figure out how to use this information to figure out my other X Chromosome matches on Gedmatch.com.

I watched the excellent moving chart at smgf.org -- http://www.smgf.org/education/animation ... osome.jspx

What should I look for to compare matches with other X matches at Gedmatch.com?

Thank you.

Posts: 7
Joined: Sun Jul 22, 2012 8:57 pm
PostPosted: Sun Dec 09, 2012 7:02 pm
Searcher wrote:I am trying to learn more about X-Chromosome matches and what you can learn from them.

There are 7 of us who match on high resolution mtDNA (HVR2) match at FTDNA. Two others are in the US and 4 are in Finland.

One of the two others in the US and I found that we share a common maternal third great grandmother. We do not match each other on autosomal either at FTDNA or Gedmatch.com, but we do have a considerable X Chromosome match at Gedmatch.com.

I am trying to figure out how to use this information to figure out my other X Chromosome matches on Gedmatch.com.

I watched the excellent moving chart at smgf.org -- http://www.smgf.org/education/animation ... osome.jspx

What should I look for to compare matches with other X matches at Gedmatch.com?

Thank you.


I have found that if you match the X without the autosomes, you may have a match that is very far back in time. Often there are many males in these lines because no crossover recombinations occurred when the X passed through each male, except at the very tips. See Blaine Bettinger's % estimations here:

http://www.thegeneticgenealogist.com/20 ... me-charts/

These probabilities are quite variable in real life. You may have a difficult time going back far enough in time to find a common ancestor.

Obviously it is very labor intensive but if you have an X match, that means you can weed out any path that shows two males in a row. That is a huge advantage.

If you want to trace a possible X from your ancestor or your matching cousin's ancestor down to the present, I have found it helpful to turn Blaine's fan charts upside down. Use the blue circle for the male X ancestor or the pink circle for the female X ancestor.

http://www.thegeneticgenealogist.com/20 ... hromosome/

Every time a descendant has multiple children, you need to start a new upside down fan chart to take into account each child. Write the names of each descendant in a box. After awhile you won't need the fan charts because you will just remember not to trace any lineage from a father to a son. Use search engines at Ancestry.com for those living in the United States. Most libraries have subscriptions.

It is much easier if you have both a robust X chromosome match along with a recent common ancestor that also shows close autosomal matching.

I recently was able to find a potential birth father for a women without knowing his name. I only knew the location of where he was living at the time he fathered a child. This was fairly easy because his daughter found an X chromosomal match with an estimated male 2nd cousin. The autosomes had multiple segment matches. By utilizing current Ancestry.com information along with knowledge about the X pattern of inheritance, I was able to find a potential great-grandmother of this 2nd cousin, then follow all of her descendants down to the 1940 census looking for the names of her grandsons. Fortunately this male was born before 1940. This particular family was suspect because they had left the location where the male cousin was from and was living out of state. It was a matter of process-of-elimination and dumb luck that I was eventually able to match geographical locations.

Even a father who does not know he is a father can sometimes be found through familial DNA testing.
Kathy

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