It's magic. I repost a message and, voila, the original shows up -- and it only
took 25 hours to make the round trip at the speed of light. Sorry for the
duplication.
I did receive a response offlist, and as the point apparently needs
clarification, I'm sharing my reply...
Yes, two brothers can be different, but normally by just one mutation event, at
least when testing only 67 markers.
The more markers you test, the higher the probability that you will find a
mutation. If you test enough markers, you'll probably find more than one
mutation. We're only testing a few dozen markers out of tens of thousands. We
could do a lot more if each of us would have our entire genome sequenced, which
would, of course, be prohibitively expensive. Thanks to the special nature of
the Y-chromosome:
http://dgmweb.net/genealogy/DNA/DNA-Introduction.shtml
we can do quite a bit with a very modest level of testing.
Diana
-----Original Message-----
From: carrico-dna-bounces(a)rootsweb.com On Behalf Of Diana Gale Matthiesen
Sent: Monday, August 20, 2007 5:25 PM
To: carrico-dna(a)rootsweb.com
Subject: Re: [CARRICO-DNA] Node Chart for Peter CARRICO I
Linda,
The mutations each subject has only to himself did happen later, in some
generation after Peter I, but before themselves. We don't know, yet, where.
The values that they all share had to have occurred before Peter I because
those
were the values he transmitted. Peter might have been carrying, at
most, one
new mutation from his father. We won't know that until we've hooked up with
his
originating family.
These subsequent mutations, in our tested subjects, could have happened in any
generation, even the current one. I have twice had reason to test brothers in
my family. In one case, the brothers matched 67/67, but in the other, they
matched 66/67. In the latter case, a mutation occurred between the father and
one of his sons. We know which one because one of the brothers matches his
cousins, while the other is off by that one mutation. In other words, one of
the brothers is modal at that marker (same value as his seven tested cousins),
while the other brother is unique in the family for that marker.
The mutation occurs during "spermatogenesis," the biological process whereby
an
undifferentiated cell in the father's testicle is transformed
into a mature
sperm (independent, with a means of propulsion). Just that one sperm carries
the mutation, so it is transmitted to just one son. From then on, the son
bearing the mutation will pass it on to all of his sons. That's how we're
able
to pin-point where a mutation took place, provided we have enough
test
subjects.
The odds against the same mutation happening twice in sperm transmitted by one
father are so astromical that it is taken as a given that any particular
mutation is a one-time event transmitted to only one son. The odds against
one
father having more than one son with *any* mutation, much less the
same
mutation, are also astronomical -- unless the father works in a nuclear power
plant... Seriously, mutations are fundamentally rare events, which is the
reason this method works.
Diana
P.S. There's something to be said for, ultimately, testing all of your living
male blood relatives. You don't know what you'll turn up. Maybe nothing
unexpected, but that's a nice outcome, too.