Hello List,
It's been my experience that if one person has a question, there are probably
others with the same question, who haven't spoken up. I was asked this question
off list, but for this reason, I hope this individual won't mind if I reply to
the entire list. Paraphrasing their question to maintain their anonymity:
I have been trying to google search an answer, but can't
come up with anything definative regarding the mutation of
marker CDYb. You have it listed as one which mutates
more frequently than some of the others, and am trying to
determine how much weight the results might carry in
defining the various lines of descent. The gist of what I'm
finding searching google is that it mutates frequently
enough that sight differences really don't tell us anything.
But, like I said, I couldn't find anything definative or
quotable. If you could point me in a direction of
something I could read...
I don't off hand know what I can point you to for something to read. Most of
the people writing about Y-DNA STR testing are working on large databases in a
paleoanthropological time frame (over thousands of years), and their perspective
is different than that of genealogists, who are working with single families
over a few hundred years. For them, fast-mutating markers are "noise"; for us,
they're important clues.
If you want an opinion other than mine, I would recommend joining the
Y-DNA-PROJECTS mailing list and asking there:
http://lists.rootsweb.ancestry.com/index/other/DNA/Y-DNA-PROJECTS.html
You might also ask at DNA-NEWBIE:
http://lists.rootsweb.ancestry.com/index/other/DNA/DNA-NEWBIE.html
FWIW, here's my opinion (speaking as a retired biologist with five years
experience running six DNA projects):
When large sample sizes and/or long time frames are evaluated, some markers do
appear to mutate more frequently than others. If you are trying to evaluate
deep ancestry (back thousands of years), you want to look at markers that are
stable or "dependable," that is, ones that *do not* mutate frequently. This is
the reason you find people ignoring not just CDYab, but the two other markers
next to it in the table, that is, DYS576 and DYS570, plus DYS464abcd, which are
also highlighted in red in the table.
In contrast, if you are dealing with a small sample size in genealogical time,
such as a single family for 10-15 generations, you find that your problem is
that everyone is too much alike -- as are we CARRICOs. Markers that are
"undependable" in long time frames, become useful indicators in short time
frames. That's the reason I'm pressing people to test DYS710 and the
palindromic pack -- these are among the most frequent mutators.
Most of the project members are 9 or 10 generations from Peter I. When testing
67 markers, you typically get a mutation *roughly* every 7 generations, which
means we'd expect most of the project members to have from 0 to 2 mutations,
averaging one. As chance would have it, we lean towards 0.
CDYb is volatile, which is why we have CARRICOs who are 36, 37, or 38 at this
marker, even though none of us is more than about 10 generations removed from
Peter I. We have three people who are 36 at this marker, and it is possible
that the mutation from 37 to 36 happened independently three times downstream of
Peter I. If we test enough cousins, we can eventually tell whether it happened
once or twice -- or three times. But it's most probable that the mutation has
happened only once because we are talking about so few generations.
So, does a value of 36 at CDYb *prove* Charles, James T., and John W. have a
common ancestor downstream of Peter I?
http://dgmweb.net/genealogy/DNA/Carrico/NodeChart-PeterCarrico.shtml#chart
No. Not until we have tested enough cousins to locate the first appearance of
the mutation and not until we have at least one solid paper trail to that
person. Is it a good working hypothesis that they are? Yes, and the
probability that this hypothesis is correct is sufficiently high that, for the
time being, I'm accepting the connection.
We are not "done" with the CARRICO DNA tree, it is just beginning to take
shape.
Unless Y-DNA STR testing becomes much cheaper or more people start seeing the
value in it, we will be at this for *years*. And unless we also continue to
make progress on our paper genealogy, we aren't going to make good use of the
DNA test results.
Whether in science or in a court room, what we are seeking is two entirely
independent lines of evidence -- paper and DNA -- proving the same thing. That
kind of independent proof is so strong, it becomes irrefutable.
Diana