How distant should cousins be before a Big-Y test is helpful?

Question

I've got a Big-Y and yDNA-111 already done for one cousin with a particular surname and he has a second cousin, once removed that has only tested yDNA-37. They have a shared brick wall that is just past their most recent common paternal ancestor, his great-grandfather. They have an haplogroup they clearly match, but the path to hook up with the other members is still unknown, but the other members all hook up to a person from the 1600s.

Is there any value in getting a Big-Y for the second cousin once removed, or would upgrading from yDNA-37 to yDNA-111 be more useful as it would help identify any recent STR mutations. None of the others on other side of brick wall have any SNP testing, just STR, several at yDNA-111, at this point.

Answer 1

In terms of financial efficiency, the Big Y is more preferrable than yDNA-111. Why? Because (let's imagine) that you got the yDNA-111 result for this particular person. You also has the result for another person. There maybe some difference in markers' values or they may be the same. But it doesn't mean anything!!! You can't state for sure when lived the MCRA!!! To get the idea when he lived you need to collect the statistical data for the whole family.

OK, I explain ambiguosly. I will do my best and try to explaim in simpler way. For example, these two persons has 1 mutation. We know that 1 mutation occur 1 time in 150 years (the precise value is not important for the example). Does it mean that the MRCNA lived precisely 150 years ago? No, no and once more - no. It is statistical value got from the populational investigations. The mutations occur sporadically.

But when we look at SNPs and particularly private SNPs from BigY, and better - FGC Y-Elite, test we can be more sure when this SNP was formed. Because every particular SNP mutate VERY rarely and usually is fixed in it's mutated state across generations (of course, back-mutations may occur but they are double rare )))

So to confirm the relationship one should to test all necessary persons with full (or almost full )) Y genome sequencing, compare all SNPs, extract the matching between persons SNPs, try to understand their formation date and make conclusions. After you extract these SNPs specific for your family, clan or branch, you will be able to make extra-test for confirming relationship of another person for belongins to your family/clan/branch. There is option to test somebody for particular SNPs in FTDNA lab and in Y-SEQ lab.