Can the common parent of half siblings be determined from sibling's DNA and...DNA?

Question

A person (the daughter)  I am working with and I have run across the following situation.

She has her test in GEDmatch.

Her biological father (proven via DNA) is in GEDmatch.

His discovered by DNA sister is in fact a half sister and her kit is in GEDmatch. This sister is a "half-aunt" of the daughter.  All confirmed by DNA and ISOGG measurements.

The daughter has created Phased kits for her mother in GEDmatch.

I have a GEDmatch kit for a close unconnected cousin of the daughter's and the father.

Can it be determined which parent of the half siblings is the common biological parent? And, if so, how.

Thanks,

 

Pete

Answer 1

If I'm understanding correctly that it's the father and the aunt whose common parent you're trying to figure out, and both the father and the aunt are in GEDmatch, compare their X-DNA. The father only got X-DNA from his mother and the aunt from both her parents, so their X-DNA should match if they share a mother and shouldn't significantly match  if they only share a father. (ETA: Unless their mothers are closely related, but that's a whole other issue.)

Comments

Yeah - I think I shoulda known that. :-(

THANK YOU

Pete