Tuesday, April 19, 2016

The Randomness of DNA, another 23andMe match with a known common ancestor

I have heard back from an individual who is sharing genomes on 23andMe with me/my account.  From my posts on this blog they were able to identify the common ancestors with Peggy, which are Joseph Tysick/Margaret Cross. This is always cause for rejoicing, so lets all take a minute and rejoice.  

Now onto the randomness part.  This individual (hereafter called "PD") is a 4th cousin twice removed. One would expect a 4th cousin ONCE removed to share an average of 6.64 cM. One match is over 39 cM and the other over 32 cM.  That means over 71 cM shared.  This is much higher than I would have expected.  

I will confess I have not spent as much time on Peggy's tree as I might have liked.  So, possibly, maybe, perhaps, there is a closer connection  or at least a 2nd connection I am not aware of ? However, PD's mother has been tested and does not appear to be a match to Peggy (I can't say with certainty, as I am not sharing with this individual) and the known common ancestor is on PD's fathers side.

And before anyone asks, no, neither of the 2 chromosome matches are on the X.

Nothing sends a genealogist scrambling for source documents than something looking not quite right.  So you can all look forward to some posts with a ton of source documents, helping me piece together various parts of the tree.

I spent part of the day filling in new cousins on Peggy's tree, descendants of Joseph Tysick/Margaret Cross.  

Looking at the completeness of Peggy's tree for the likelihood that there is another connection we have missed shows me I do indeed have work to do on this tree! 

Peggy's "Ancestor score" is: (generated by HistoryLink from her Geni tree)

2/2 parents
4/4 grandparents
8/8 great grandparents
12/16 greatX2 grandparents
10/32 greatX3 grandparents
8/64 greatX4 grandparents (eeks, really? I'm taken aback by this)
12/128 greatX5 grandparents
16/256 greatX6 grandparents
27/512 greatX7 grandparents
49/1024 greatX8 grandparents
106/2048 greatX9 grandparents

I updated Peggy's profile in GenomeMate, and indicated the MRCA on the 2 matching segments with PD.  I then began working on the conclusions on the other matches in those segments.

More on this soon!