The Missing Shared Matches–Part II

The testee in “Missing Shared Matches” (using the autosomal DNA test at  AncestryDNA) had two close maternal relatives that also tested:

• the grandson (referred to as A) of his mother’s sister
• the grandson (referred to as B) of his mother’s mother’s brother

The testee obviously will have shared DNA matches with both A and B. The testee, A, and B share a set of great-grandparents (Louis and Marie). The testee and A share a set of grandparents (William and Mary). Mary is the daughter of Louis and Marie.

The testee and A should have more shared matches that the testee does with B. A is more closely related. On paper:

• A and the testee should have 1/2 of the same genealogical ancestry–they share two out of four grandparents, four out of eight great-grandparents, etc.–because their mothers were siblings
• B and the testee should have 1/4 of the same genealogical ancestry. They share two out of eight great-grandparents, four out of sixteen great-grandparents, etc.

The paper percentages are a guideline of shared DNA and proportions of shared matches because:

• the amount of DNA you inherit from a great-grandparent may not be exactly one-eighth of your DNA–it’s been split and passed a few times by the time it gets to you.
• shared matches at AncestryDNA depend upon the size of your family, how many relatives have tested, and how much DNA the testee got from a specific ancestor

So just because A and the testee have 1/2 of the same paper pedigree and that the testee and B have 1/4 of the same paper pedigree does not mean that the number of shared matches B has with the testee will be half of what the testee has with A.

But when the shared matches were reviewed there was a problem.

The shared matches the testee had with A and the shared matches the testee had with B were all the same or could be traced to a relative of Louis and Marie. The testee had no shared matches with A that were not also a match with B or who could not be shown to be a relative of Louis and Marie.

Louis and Marie were ethnic French-Canadians born in upstate New York. William was born in Chicago.

But shouldn’t the testee and A have shared matches with each other that are not shared matches with B?

Stay tuned.