37 marker test results question

[jimgilmer]

There are three Gilmore Y-DNA testees who completed 37 marker tests. They are R, D and J.

R & D have paper trails that show the same MRCA (Gilmore surname) 5 generations back. J cannot connect with any paper trail to the Gilmore lines of R & D.

The test results show these comparisons:

R & D are 5 markers off on the 37 marker test.

R & J are 3 markers off on the 37 marker test.

D & J are 6 markers off on the 37 marker test.

Why would R & D be 5 markers off if they have a common ancestor 5 generations back? It would seem to me that they should be close to a perfect match, assuming their paper trail is correct.

[rucksack]

Are all of these people tested through FTDNA?

Have you actually seen the STR results, or are you basing your statement regarding GD on ysearch entries that they have perhaps manually done?

[MMaddi]

Since yDNA mutations are random, but with known mutation rates with a range of probabilities, the case you outline is possible. However, you are right that, with a common ancestor 5 generations ago according to the paper trail, it would be expected that R and D would have a genetic distance of perhaps 2 or 3, not 5.

Any speculation about the relationships among R, D and J without looking at the specific results is probably not going to be able to say anything useful that would answer your question. Are the results located in the results table for the Gilmore Project, at http://www.familytreedna.com/public/...ction=yresults? If so, what are the kit numbers for R, D and J?

[jimgilmer]

Yes, the results are posted on the Gilmore FTDNA Surname Project:

R is kit number 101614

D is kit number 59414

J is kit number 166844

Take a look and see what you think.

[MMaddi]

Yes, the results are posted on the Gilmore FTDNA Surname Project:

R is kit number 101614

D is kit number 59414

J is kit number 166844

Take a look and see what you think.

Comparing these 3 haplotypes in the McGee Y-DNA Utility (at http://www.mymcgee.com/tools/yutility.html) gives a "time to most recent common ancestor" (TMRCA) between R and D of 27 generations, between D and J of 32 generations and between R and J of 17 generations.

This is at the 50% confidence interval, sort of the midpoint of the probability curve. At the 10% confidence interval (very unlikely) TMRCAs are:

R and D - 15 generations
D and J - 19 generations
J and R - 8 generations

It looks like your instinct about this situation was right. It doesn't look like R and D are as closely related as their paper trails indicate.