DNA half-sibling

Question

My brother did an Ancestry DNA test last year and last week got notification of a new close relative match. The man matches at 1695cM which indicates grandparent/grandchild/uncle/nephew/half-sibling. I've determined the age of this person which rules out the grandparent/nephew/grandchild and he doesn't match with our maternal Aunt or cousin.

We thought perhaps it was a child my Father had that we didn't know about.However, when I contacted a paternal cousin who had completed her DNA to asked her the level of connection with this person he doesn't show on her matches. As the conversation progressed we realized that NONE of my paternal relatives with DNA test are showing as matches for my brother. So.....where does that leave us? After I realized this I thought it was possible that my Brother might be a half-brother fathered by another man, but the new match doesn't match with my maternal side.

If he were an uncle he should be matching up with one side or the other. All of the parental units are deceased so further testing is not available. I've ordered a DNA test for myself but not sure it will clear up matters much and might add more questions. Any ideas?

Answer 1

If your brother has a different biological father than you, then the new match would most likely match with your brother's bio-dad, and no reason they would match your maternal side. You might want to get a DNA test yourself, to verify the half-brother relationship (and anticipate the possibility that you may actually be full siblings, but not via the father you know).

Assuming your brother has a bio-dad different from your father, you would need to treat this the same as an adoptee seeking biological parents. This would involve identifying the bio-dad through common ancestors in the pedigrees of your brother's non-maternal DNA matches. You have the advantage that you already know who the mother is, with all the hints of time and place that provides.

There are groups on Facebook whose members can help with the specifics of this sort of search ("Genetic Genealogy Tips & Techniques" and "Genetic Detectives" come to mind, I'm sure there are others as well).