Select Page

Confirming Isabella

Another solid X-match

It’s always comforting when the DNA evidence matches the paper trail.

Especially when you’ve spent as much time researching a paper trail as The Legal Genealogist has spent on her second great grandmother, Isabella (Gentry) Robertson.

Isabella is a challenge for a lot of reasons.

Start with the fact that she was married before the 1850 census1 and so was never enumerated in her father’s household.

Go on to the fact that she was born well before Mississippi starting keeping birth records,2 likely married in a burned county in Mississippi,3 and died in Texas before death recordation was routine there,4 and you start to see the problems.

Oh, and family records give her any one of three (or more) possible maiden names.5

So any time a cousin DNA tests and matches exactly the way he or she should match if our conclusion about Isabella is right… we breathe a sigh of relief.

Which we did this week with cousin Wayne.

Wayne is my third cousin, descended from Isabella through the third of her 11 children, Bird Alexander Robertson. Wayne’s line goes through his mother, his grandmother, then his great grandfather Bird who was Isabella’s son. Mine and that of my siblings is through our mother, grandmother, and great grandfather Jasper, Isabella’s youngest.

And I have a history of not matching third cousins, even when they match everybody else in my family.6

So when Wayne’s DNA results showed up on Gedmatch and we were able to do a thorough comparison of the data there, it was truly comforting to see the numbers line up all the way across the board, just the way they should.

Using Blaine Bettinger’s Shared cM Project data from August 20177, the expected amount of shared DNA between third cousins is 53 cM, the average 74 cM and the range 0-217. Wayne and I share 57.6 cM.

Even better is the fact that we all have a match on the X-DNA chromosome — because that leads directly to Isabella.

You see, because of the way the X chromosome is handed down, there are fewer ancestors who could possibly have contributed DNA to that chromosome. In a male, for example, only his mother’s ancestors could have contributed since he only gets an X from his mother (he gets the Y that makes him male from his father).8

And when you chart out the X-DNA could match, using my brothers (because they have fewer options than I have for ancestors who gave them X-DNA), it’s one of those “ding ding ding we have a winner” moments.

Here’s Wayne’s chart:

And here’s the chart for my brothers:

Circled in red, on both charts, is Isabella.

I love DNA.

At least when it agrees with my paper trail…


Images: X-match charts, courtesy Blaine T. Bettinger, The Genetic Genealogist

  1. 1850 U.S. census, Winston County, Mississippi, population schedule, p. 373(A) (stamped), dwelling 809, family 816, Isabella “Robinson”; digital image, ( : accessed 30 Aug 2013); citing National Archive microfilm publication M432, roll 382.
  2. See FamilySearch Research Wiki (, “Mississippi Vital Records,” rev. 23 Aug 2017.
  3. See “Museum Memories,” Neshoba Democrat, 3 Oct 2012 ( : accessed 16 Sep 2016).
  4. See FamilySearch Research Wiki (, “Texas Vital Records,” rev. 6 Apr 2017.
  5. One set of family notes says she was a Pugh. One child’s death certificate says Rankin. And two say Gentry. Sigh…
  6. See generally Judy G. Russell, “Another darned mismatch,” The Legal Genealogist, posted 21 July 2013 ( : accessed 17 Sep 2017).
  7. See Blaine T. Bettinger, “The Shared cM Project – Version 3.0 (August 2017),” The Genetic Genealogist ( : accessed 16 Sep 2017).
  8. See generally Judy G. Russell, “X marks the spot,” The Legal Genealogist, posted 5 Jan 2014 ( : accessed 17 Sep 2017).
Print Friendly, PDF & Email