Hello List,
To answer another of Berny's questions, as to how distant CARRICO
cousins can be matching 67/67 because, isn't everyone's DNA unique?
http://dgmweb.net/DNA/Carrico/CarricoDNA-results-HgJ2a4b.html#data
Yes, it's true that everyone's DNA is unique, but that's in reference
to out *entire* genetic endowment: both sex chromosomes, all 22 pairs
of autosomes (non-sex chromosomes), and our mitochondrial DNA. For
the CARRICO project, we are only using a few dozen markers (locations)
on just the male Y-chromosome.
The 13 markers used in CODIS, the FBI criminal identification system,
are on autosomes (plus an AMEL test on the sex chromosomes to
determine gender):
http://en.wikipedia.org/wiki/Combined_DNA_Index_System
You inherit a mixture of autosomal DNA from your mother and father,
and only identical twins will inherit the exact same set of marker
values. And, yes, this means identical twins could not be separated
-- or separated only with difficulty -- using their DNA.
It may seem that 13 markers are not a lot to determine one's identity,
but the probability of two people having the same values at all 13
markers is infinitesimally small. Even if only two different values
are possible at each marker -- I don't know the real number, but it is
surely more than two for each marker -- the probability would be one
in 2 to the 13th power, a very small number. Looked at another way...
If you flipped a coin 13 times in a row, what is the probability that
you would get the same result (heads v. tails), in the same order,
*twice*? Definitely not betting odds...
In contrast, the Y-chromosome is being handed down, mostly intact,
though with an occasional random mutation, from father to son down
through the generations. The reason Y-DNA testing has limited use in
forensic science is the very fact that many men in the same family
will have the exact same result, making it impossible to use as proof
of unique identity in a criminal prosecution.
Diana