2nd cousin

I have read all of Peter's articles on DNA, and have tried to follow most of the discussions, but am still not certain if any DNA test would help in my case. There is some contention within the family if another supposed great granddaughter (Mary) of a great grandfather is related and we wondered if a DNA test could shed any light on this. I'm confused as Sarah's relationship is through her mother and her father, whereas Mary is through her father and his father - it would be simpler I think if it were purely through maternal or paternal line. Has any one any thoughts on this, if Mary & Sarah did a DNA test would it show if they were related?

 

An autosomal DNA test would be the one to try here, and with 2nd cousins I think there is a pretty good chance that this will show if Sarah and Mary are related or not. We don't inherit DNA from all our ancestors, so it's possible to be related and not share matching DNA, but the closer the relationship the less likely this is to happen.

 

Slightly less for a half blood 2nd cousin, presumably, which I think is what we may be talking about here, but still pretty good. My match with a half blood 2nd cousin is more like a 3rd cousin match.

 

I have a match with a 3rd cousin who is estimated to be a 4th-6th cousin (Ancestry's estimation), because he is technically a half cousin (me descended from a son of my g-g-grandfather's first marriage; him through the second).

And on the same side of the family my father has a 2nd cousin (different cousin from above), who Ancestry estimates is actually a 5th - 8th cousin, which is another half cousin - from the same two sets of relationships: my g-g-grandfather's first and second marriages!

I have been in contact with both, and the relationships are crystal clear, so I figure the "half" portion is why Ancestry's estimations are so far out!

 

Not that I've noticed Peter - but I do unfortunately have a few instances of places where the bride and groom share the same surname before they're married, often because they're some degree of cousin...

 

Well, the one in my direct line was a pair of my Dutch Jewish ancestors, so there is an element of marrying within the religious community. Other than that, I'm not completely sure - one family group that intermarried a lot lived in and around Wisbech, Cambridgeshire and the other that I've discovered that intermarried lived in and around Minsterworth, Gloucestershire.

I am not familiar enough with the terrain of those two places to comment on isolation - one group at one point where Non-Conformists (the one around Wisbech), but I don't think that had anything to do with it, since that family group at one point lived in London and Surrey before moving into Cambridgeshire - that group did also intermarry within a group of other families which I think ties in with the Non-Conformist period. I haven't really discovered anything else in my research so far that would suggest any other social or cultural isolation.

 

Most definitely!

 

Thank you all for your replies. The half-second cousins involved have decided not to go down the DNA test route - they are sure they are related, but even if they aren't they would remain great friends and help each other with their research.