Friday, August 25, 2017

DNA Randomness: Siblings

If you have been researching genetic genealogy for any length of time and I guess more so if you have also taken courses or attended webinars,  you have heard about the randomness of DNA as it pertains to autosomal DNA inheritance.  While we each get 50% of our DNA from our father and 50% from our mother,  the 50% that we get from each parent is not the same 50% when comparing to other siblings(unless you are comparing Identical Twins).  I have 4 full siblings, only one of which has tested.   Even with just one having tested I can see that is true in comparing our matches and the amounts she and I match them.  Our Mother has tested also, so I have phased kits created at GEDmatch using her results in comparison with mine and also phased kits comparing her results to my sister's results.  These are very useful.

Ancestry has a phase filter which you can use if one or both parents have also tested at AncestryDNA.  Since I only have one parent that was able to test, that tool lets me see a listing of matches who are also a match to my Mother.  Keep in mind the match range is similar to Shared Matches tool in that it only includes 4th cousin and closer matches---not Distant Cousins.  It would be nice if they could do a list of 4C or closer who DO NOT MATCH when there is only one parent who has tested.

The chart below compares my match list with that of my full sister.  I did not include our Mother's results for our maternal matches nor the matches of my daughter.  I may do that in a future post  Those covered are matches who Ancestry DNA estimated were in 3rd cousin range for at least me OR my sister.

The RED border is around those who were in my list at 3rd Cousin or above.
The VIOLET border is around those who were in my sister's list at 3rd Cousin level.who were ranked as 4th cousins by Ancestry in my list.

Average Difference 65 cM

Notes:  Both of our parents have Colonial American Ancestry.  Pretty much all of our ancestors were in the US before 1800.
Our Distant Cousin matches Start on:
Page 41 of 876 (Becca)---- 30 matches which are 3rd Cousin or closer
Page 38 of 908 (Marie)-----26 matches which are 3rd Cousin or closer
Marie:  1873 4th cousin or closer matches
Becca:  2007 4th cousin or closer matches

GEDmatch comparison:  Marie and Becca
Largest segment = 145.6 cM
Total of segments > 7 cM = 2,507.6 cM
51 matching segments
Estimated number of generations to MRCA = 1.3
Six of my matches that were estimated 3rd cousin were in the 4th cousin range for my sister.  Eight of my sister's matches that were estimated 3rd cousin were in the 4th cousin range for me. There was one match who was on the low end of a 3rd cousin match for my sister who was in my Distant Cousin match.

Ancestry's Cousin Categories
From the Hyperlinked "What does this mean?" in the Amount of Shared DNA info box

A bit confusing I guess as there is a gap between categories. I did check for ours that fell
in the gap(195 cM) and it was noted as a 3rd cousin.

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