Are You My Daddy?

September 24, 2015 10:14 AM

Asking for a friend: "There is some question about who my father is - the man who raised me (Daddy) or his brother (Uncle) The only family DNA I have is from my nephew who is my sister's son, definitely Daddy's grandson. My nephew and I share 1610 cM. Is this enough information to determine who my father is?"
posted by Allee Katze to Science & Nature (5 answers total)

Based on the charts here, there's not enough information to determine definitively. If you look at the range of values for each relationship, they can differ by quite a bit.
posted by demiurge at 10:36 AM on September 24, 2015

Yes, I don't think that's really enough; it's tricky because the range for a nephew via a half-sibling and a nephew via a full sibling would overlap by quite a lot.
posted by mskyle at 10:40 AM on September 24, 2015

I believe sharing 1610 cM is about a 23.7% relatedness match (based on 6770 total cM). A full nephew would share 25% and a half-nephew would share 12.5% -- these are averages, but I'd lean toward him being the full nephew (unless the nephew's father is somewhat significantly related to your genetic line, which would increase the genetic kinship without changing the factual kinship).
posted by melissasaurus at 10:56 AM on September 24, 2015 [1 favorite]

I think maybe melissasaurus missed that the two possible fathers were brothers - the statistics in that table, I believe, assume that the parents of half-siblings are not related to each other. I'm not 100% sure but in this case I think a full nephew would share 25% but the half-nephew would be at 18.75%.
posted by mskyle at 12:09 PM on September 24, 2015

Best answer: I think maybe melissasaurus missed that the two possible fathers were brothers

Oh yes, I didn't take that into account. So the sisters are either full sisters or 3/4 sisters. Meaning the nephew is either a full nephew or a half nephew/half first cousin once removed. 3/4 siblings share ~37.5% so a 3/4 nephew would share around 18.75% as mskyle said. This brings it into murkier territory, but I'd still lean toward full siblings/full nephew.
posted by melissasaurus at 1:08 PM on September 24, 2015