Monday, June 23, 2014

Can DNA Point to One Ancestor?

This is an open-ended blog post with questions. However, this scenario shows how X-chromosome matches in 23andMe can possibly pinpoint one ancestor as being the connection to a DNA match.

Lisa, a new DNA match in 23andMe, shares DNA with me, my father, and five Ealy-Kennedy cousins. The range is from 16 to 39 cM. She is a predicted 4th cousin to my father and me, with whom she shares 18 cM across 1 segment. Lisa also shares DNA across two segments with three of us. All seven of us are direct descendants of my great-great-grandparents, Bob & Jane Ealy and Lucy Kennedy (and the white father of Lucy's childrenof Leake County, Mississippi. Three children of Bob & Jane Ealy married three of Lucy Kennedy’s children, and we all descend from one of those three Ealy-Kennedy couples.

What makes this match to Lisa even more interesting is because she also shares segments on the X chromosome with two of us. Lisa shares 18.8 cM on the X with my cousin Violet and 39.1 cM on the X with my cousin Christopher, an adoptee. We know that Christopher descends from one of the three Ealy-Kennedy couples via his unknown maternal grandfather, but we don’t know how, yet. (See "Help Us Find Christopher's Birth Mother.") Christopher also shares X-DNA with Violet and our cousin Nenise. See the following comparisons:

Utilizing the female X inheritance chart, I was able to deduce that Lisa is related through either of the following two ancestors:

Jane Parrott Ealy, who contributed up to 25% to Violet’s X-DNA, or
Lucy Kennedy, who contributed up to 12.5% to Violet’s X-DNA.

I checked the chromosome view in 23andMe, and both of Lisa's two X-chromosomes are 100% West African. Therefore, Lisa’s matching segment on the X with Violet came from ancestors of African descent. Lucy Kennedy was “mulatto,” born to an enslaved African-American mother (Jennie) and an unknown white father. A deceased family elder recalled family members saying how she "looked like a white woman." She inherited her X-chromosomes from her Black mother (50%) and from her white father (50%).

Therefore, my questions are the following:

Since Lucy Kennedy was “mulatto,” does that lessen the chance that the matching X-DNA segment came from her?

Does the amount of Lisa’s X-DNA sharing with Violet and Christopher (18.8 & 39.1 cM) negate Lucy because she possibly contributed so little (0 to 6.125%) African DNA to Violet’s X-DNA?

Does this DNA analysis point to Jane? Your feedback is greatly welcomed.

Presently, Lisa doesn’t know of anyone in her family being from Leake County, Mississippi. Her paternal roots are from Rapides, Avoyelles, and Allen Parishes, Louisiana. Her maternal roots, of which she knows very little, hailed from Oktibbeha, Winston, Holmes, and Sunflower Counties, Mississippi. Coincidentally (or not), Jim Parrott (born c. 1834), who I strongly believe was Jane’s brother, moved to Holmes County before 1900 with his wife and large family. Hopefully, she and I can figure out the connection soon.

Lessons that I am learning from feedback of this post:

(1) Even though one female is mulatto, she could have passed her predominantly African segment down to a child in its entirety or she may have passed down a mixed mostly African X, that when recombined in the next generation, became a wholly African X. Also, 39 cM only comes out to about 0.57%, so it is definitely possible for that amount to have come from someone from whom you can inherit up to 6%. (Lisa Landrum)

1 comment:

  1. I'm thinking that in certain cases it COULD point to a particular ancestor, but in this case you really can't choose one female over the other based on the fact that the segment is African. Even though one female is mulatto, she could have passed her predominantly African segment down to a child in its entirety or she may have passed down a mixed mostly african X that when recombined in the next generation became a wholly african X. Unless you can find someone who is related to only one of the two women and make a match with them on that segment, i think its impossible to know which woman the segment is from. Also, 39cM is about .57% so it is very possible to have inherited that amount of dna on the X chromosome from someone who you could inherit up to 6% from.


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