Closely related or not?

[npmcl]

Some time ago a male member of my family and a possible relative with the same surname with ancestors from the same city (1700) took a 10 marker test from another company, it resulted in a perfect 10/10 match. We were pleased that we were related and that our MRCA was probably not far distant.

We decided to confirm this by taking the FTDNA 25 marker test unfortunately this showed 1 mismatch at 464d ( 17, 16) so we were still related but our prospects for finding the possible generation of the ancestor appeared to move back a bit.

Now we have taken the 37 marker test which has shown two more mismatches 576 (18, 20) and CDYb (39, 38). Now we have four mismatches and are "probably related" and of course the generation of any MRCA has gone back even more. I understand that the mismatches are of fast changing markers although I'm not sure how that really affects the results..

So according to FTDNA we have gone from "the probability of a close relationship is very high" to "Probably Related" with the need to test more people. I'm just confused.

Noreen

[dennis]

Noreen:
When we apply the statistics of mutation rates to individual cases, the interpretation becoms a little cloudy. This is because mutations occur randomly, and are unpredictable. We have cases of first cousins that differ by two mismatches.
If you have two people with the same surname from the same city in 1700 that match 33/37, you should pursue the paper trail in an attempt to find further evidence. How large was the population of the city? If the population was small, that increases the probability of a relationship (in my opinion). How common was the surname, if it is somewhat rare, that would also add to the probability of a relationship. Have you looked at marker frequency? If they share any rare markers,
that would also increase the likelihood of a relationship. If you could find additional descendents to test, that could provide insight into the possible relationship. The more distant the relationship, the better (it would not be useful for example to test a brother, first cousin, or uncle of your male relative).
Dennis West

[npmcl]

Thanks for your answer Dennis. We do have a third person, same surname from nearby area who is now doing the 37 marker test, this person matched 24/25 to one of the people and 23/25 to the other in the 25 marker test. We have all reached a point where the paper-trail is very difficult however we are trying to progress.

I'm not sure of the population of the city in 1700 (Bradford, WR Yorkshire, England) but the surname (Clough) was not uncommon in the area. It is actually a dialect word from that area meaning ravine. No rare markers I'm afraid, all R1b.

Noreen