On 2008.03.05, Bob Kosovsky <kos@...> wrote:

Has anyone figured the probability of this kind of situation - where
both a Y-DNA and mtDNA match points to the same person?

I also have a mtDNA match who matches my maternal grandfather's
line, which is a similar, though not an exact, situation to yours.
I would think the phenomenon where a person matches both Y-DNA and
mtDNA to another person is not a rare occurrence. There were many
instances of brothers in one family marrying sisters >from another
family (or brother-sister >from one family marrying sister-brother

from another family) as well as cousins marrying cousins, so when

you calculate how many ancestors a person has in the last n
generations, the number will be much smaller than 2 to the nth
power.

I don't know a lot about population statistics, but I would think
that if (big if!) enough people >from a given region had their DNA
tested so that most of the haplotypes >from that area are
represented, and we know what the population was, the chance of a
person being a mtDNA and Y-DNA match to the same person could be
estimated. Another way to think about it- if we go back far enough,
most of the people in a relatively isolated region would be related
to each other; what proportion of those would be related to each
other on both the direct paternal and direct maternal lines?

I will take a wild stab at a guess: 5% to 10%

Judy Simon