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Old 13th June 2018, 12:31 PM
MoberlyDrake MoberlyDrake is offline
mtDNA: T2b5 | Y-DNA: J-M172
Join Date: May 2010
Posts: 1,533
It can change at any generation. If you could test your father, grandfather, great-grandfather, you might find it has changed between one of those generations. You can also have back-mutations where it mutates back to a previous value.

The Y-DNA of many Hampton men descended from a certain immigrant tend to be the same, but my cousin has a mutation in one marker and his 3rd cousin has a mutation in a different marker. Both mutations apparently occurred at some point between them and my 3rd great-grandfather.

It's random. Average numbers of generations between mutations in various markers have been computed, but they are only averages. I believe I read of a case where a father and son differed on 3 markers.
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