How many markers

[sarahmj]

Hello all,

If I wanted to prove (or disprove) a relationship between 3rd cousins that share the same male ancestor, how many markers would be enough to test this relationship?

I am from Australia and I have been in contact with a possible branch of the same family in the USA, if we can both have a male tested, I'm hoping we can determine if we share the same ancestor....any additional suggestions would be appreciated.

Regards

Sarah

[MMaddi]

You need to test at least 37 markers, but 67 would be better. Make sure that both men test at the same number of markers to compare them at that level.

I'm assuming that in this case both men are paternal line descendants of the man you're trying to prove is the common ancestor. If not, you need to find a paternal line descendant (son, paternal grandson, paternal grandson's son, etc.) in each line to test.

If you can't find paternal line descendants in both lines to test, you'll have to use Family Finder, which tests autosomal DNA. That's not specific to the paternal line, since it tests the 22 pairs of autosomal chromosomes. But that type of test does find about 90% of any 3rd cousins who are in the database. Any 3rd cousins found can be from any the lines in the family tree, not just the paternal line. It will be more difficult using Family Finder to prove that the common ancestor was the paternal line ancestor.

[Jim Barrett]

Hello all, If I wanted to prove (or disprove) a relationship between 3rd cousins that share the same male ancestor, how many markers would be enough to test this relationship? Regards Sarah

Y-DNA, even 12 markers, can prove that you don't share a common paternal ancestor - if you are in different Haplogroups.

A close match at 37, or even better, at 67 markers can indicate, not prove, that you do share a common paternal ancestor. At best it will only indicate a possible distance to that relationship. It is good supporting evidence but it is not proof. As with all genealogy you need more than one piece of evidence.