07 January 2014

X-Chromosome Browser Success!

Within minutes of Family Tree DNA releasing the X-chromosome information to our Family Finder webpages, I was able to determine which ancestor gave Rebecca, my second cousin, and I a portion of our X-chromosome.

Rebecca and I matched on our X-chromosome at these two points:

Start location             End location               cMs                 SNPs
  45611715                    69267006                  14.32               1575   
 114784651                  141333316                  39.54               3575   

How did I find the most recent common ancestor who contributed these segments so quickly?

First of all, I knew this cousin was on my mother’s all-female line.  BUT, more importantly, I used Blaine Bettinger’s female inheritance fan chart for the X-chromosome to determine which ancestors could have contributed this portion of our X-chromosome to each of us.

This fan chart for women is different than for men so download each copy.  The women's if found here. The men's can be found at this website. If you prefer a list of ahnentafel numbers for your ancestors who provided your X-chromosome DNA see this site for Ann Turner's list.  I make an ahnentafel chart and omit all but the numbers in Ann's list.  This is forwarded to my matches for their convenience.

Note the pink and blue areas for the female inheritance in the chart below.  These are the only ancestors who could have contributed to any portion of a female’s X-chromosome.  Like any pedigree chart, you enter the names of your ancestors in the respective places.  I have completed one for quick reference.

For this comparison, I plotted my lineage on the fan chart as seen in the expanded portion of the chart below.

As I know Rebecca is on my mother's line, I focused only on that area.  I received my X-chromosome from my mother Beverly who received it from her mother Emily.  Emily, my grandmother, received one X-chromosome from her father Lowry and one form her mother Mary.  SO, which X-chromosome provided the portion I received that matches Rebecca…Lowry or Mary’s?

To answer that question, I plotted Rebecca’s lineage as below.

As you can see the only common ancestor who could have provided this X segment to each of us was Mary.  For Rebecca, Lowry did not contribute to her X-chromosome since Lowry could not give his copy of his X-chromosome to his son Robert.  However, Robert gave his X-chromosome that he inherited from his mother Mary to his daughter Margaret.  Margaret gave this X-chromosome to her daughter Rebecca. (Note that for a female, the X-chromosome from her mother can recombine or mix with the X from her father, but in this case we know we are dealing with Rebecca's maternal line.)

As there are two segments that Rebecca and I share and we only have Mary as a common ancestor, both segments came through her.  However, without additional matches along Mary’s X-chromosome inheritance lines, we cannot be certain which of Mary’s ancestors contributed.  It is possible that each of the two segments inherited by Rebecca and Emily from Mary were from two of her ancestors, but there is no guarantee these segments are intact as the two X-chromosome women receive can recombine (mix) like other autosomal DNA. Finding others who match Rebecca and Emily in this area may provide clues as to which ancestors gave this portion of their X-chromosome to Mary since the other matches could relate farther back in generations.

Family Tree DNA has provided genetic genealogists with a new toy for the New Year!  Thank you, FTDNA.

NOTE:  Any success story is something to celebrate.  Share your DNA successes here by emailing me.


7 Jan 2014

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