How much dna did I get from Abigail seven generations ago?

+6 votes
183 views
My grandfather was Stawyer Summerfield son of Sampson Summerfield, so how much dna did I get from Abigail Grubb?
WikiTree profile: Abigail Summerfield
in Genealogy Help by
retagged by Eowyn Walker

1 Answer

+4 votes
Seven generations back you have 128 ancestors, so you would receive less than 1% (about .78) of your DNA from any one ancestor. Dilution is one reason why "family finder" tests are not reliable beyond 3 or 4 generations. Another reason is autosomnal tests are influenced by common environmental factors and the further you reach back in time the greater the commonality from environmental exposures.
by Michael Tyler G2G6 Mach 2 (20.7k points)
edited by Michael Tyler
Thanks for the great answer, Michael.
I think the answer of .78 is correct if the question is restricted to autosomal DNA. It gets more complicated for the mtDNA, yDNA and X-Chromosome. The answer for these other 'types' of DNA are dependent on the specific sex of the children along the seven generations.
  • yDNA: 100% If it is seven generations along a paternal line. 0% otherwise.
  • mtDNA: 100% If it is seven generations along a maternal line. 0% otherwise.
  • X-Chromosome: ?% The answer is dependent on the specific sex of the children along the seven generations. I just checked and WikiTree does this calculation correctly. Sometimes the answer is .78 and sometimes it is not.
I realize Autosomal DNA is the bulk of the DNA, so .78 is always close to the correct answer. However, I think these other types of DNA are much more interesting than autosomal DNA, and much more useful for WikiTree.
Your percentage of autosomal DNA inheritance beyond your grand parents is variable.   You likely don't have any autosomal DNA from some of your ancestors 7 generations back.

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