DNA conundrum - need help

+3 votes
98 views
Maybe someone out there in the Wikitree world who understands DNA can help us.

I recently was contacted by two sisters who should be my second or third cousins, but our Ancestry DNA shows no match at all.  Yet they match my confirmed second cousins.

I am descended from George Marion Stewart who had 13 siblings.  His father was Luther Stewart, who was illegitimate and father is as yet unknown. Luther's mother was Sarah Elzabeth Stewart.  I am a DNA match to:

* Jennifer who is the granddaughter of George's sister, Annie Demarius

* Ken, who is the grandson of George's sister, Sarah Fannie

* Waymon who is the grandson of George's brother, Joseph Edward

* Waymon's sister, Annette, who is the granddaughter of George's  brother, Joseph Edward

* E. L. who is the great grandson of George's sister, Lavonia

* M. L. who is the 2nd great grandson of George's sister, Lavonia

The two sisters who contacted me are descended from Sarah Elizabeth Stewart's brother, Francis Marion Stewart/Stuart.  They are a DNA match to Ken and Jennifer, but not to me.

How is it possible that I do not have any DNA in common with the sisters?
WikiTree profile: Luther Stewart
in Genealogy Help by Carolyn Martin G2G6 Pilot (226k points)

1 Answer

+6 votes
 
Best answer
These sisters are decended from a common ancestor 2 generations back from George so you are probably 4th or 5th cousins once or twice removed.

Once you get further back than 2nd cousins then the chances of matching DNA decreases even if you are biologically related because of the random way that DNA is passed on
by Michelle Wilkes G2G6 Pilot (142k points)
selected by Edison Williams
When i get back to my pc i'll explain in a bit more detail
Thanks, Michelle.
So George is your grandfather so the people you match who are grandchildren of George's siblings would be your 2nd cousins.

Any great grandchildren of George's father Luther would be 2nd cousins.

Luther's mother Sarah is your 2x great grandmother and any great great grand children would be 3rd Cousins

so any great great grandchildren of Sarah's siblings would be 4th Cousins

That means the two sisters descended from Sarah's brother (assuming they are the same generation as you) would be your 4th cousin. If they are the same generation as your mother, they would be 4th cousins once removed to you.

See

https://www.familytreedna.com/learn/autosomal-ancestry/universal-dna-matching/probability-relative-share-enough-dna-family-finder-detect/

At the 5th cousin level you have about 10% chance of matching by DNA even if you are biologically related

at the 4th cousin level it is 50%

Different segments get passed on but not all segments get passed on to all descendants.

This is a useful chart

http://roots4u.blogspot.co.uk/2015/01/centimorgans-or-percentages.html
Thanks so much, Michelle.  That makes it much more clear.
I just edited my answer as I think I was a generation out and had to draw it out on paper lol

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