First, a couple of announcements: A second tester from CF07 has ordered his Big Y. The Most Recent
Common Ancestor (MRCA) is John A Cooley (1753-1794), married to
Rachel Kinchen(?). Just as they share an ancestor
in John, the testers' shared Y-DNAmutations would have come
from him. Therefore, once the results come back and are analyzed, we will
have a specific DNA profile for John, a profile that others can test for
without the great cost.
And a second descendant of Benjamin Cooley of Springfield, MA has volunteered for the Big Y.
In a few months, we'll have a specific profile for him, one that will fill
in some of the obvious gaps in the Y-STRs in CF02 (see the Cooley DNA Project).
Things to know:
The Y chromosome contains the male sex gene
Women do not carry a Y chromosome
A male passes his Y, unchanged, to each of his sons
Y inheritance, then, is very straight forward:
The Y holds about thirty-five million tiny molecules called bases.
These bases are comprised of one of four chemicals, abbreviated to A, C, G
or T. Now, remember that our cells regularly divide into cloned copies.
This division continues through the reproduction cycle, from the making of
sperm and eggs to the development of the zygote, the embryo and the
child—one generation after another. It might be said that we're
merely carriers for our immortal DNA, which has survived from the beginning
of life and, hopefully, will survive long into the future.
But something happens to the Y every several generations—a tiny
mutation occurs on one or more of the bases and its value (A, C, G, or T)
flips to another. This is called a mutation, or SNP. Can you spot a
From: A C C T G T T A
To: A C C T A T T A
This mutation would have occurred with the production of a sperm cell
belonging to a specific man—perhaps even thousands of years ago. If a
son inherits it, he passes it on to all his sons, and so it goes. A new
"line" of Y chromosomes has been created, one that is distinct from
all others. Over the period of hundreds of thousands of years enough
mutations occurred that we can build an elaborate as I've done with this
simple tree for some of our Cooley families:
Many of us know enough about our recent ancestry that we can say things
such as "I'm half German and quarter Italian" or even "I'm sixteenth
Cherokee." We all understand that this person has a parent of German
descent, a grandparent who is Italian and a great-great grandparent who was
Cherokee. But if we slightly rephrase it as "my DNA is half German, quarter
Italian, and sixteenth Cherokee" an obvious fact stands out: the more DNA
you share with someone the closer you're related to them. We see this same
relationship represented with "first cousins," "third cousins," etc. The
degree of distance can likewise be determined by looking at a family tree.
The closer on the tree two people are, the more DNA they share—simply
because they share a larger number of ancestors.
Of course, because the Y chromosome is passed down only through the
single father-line, which is just a tiny thread along our ancestry, there's
only one "ethnicity" represented. But something similar occurs: just as
sharing more ancestors means a closer relationship, the more shared
mutations means likewise. This is because these mutations occurred at the
births of specific individuals along the tree, whether we know their
identities or not. We might as well call YP609, YP4248, and BY3233 Tom, Dick, and
Harry. Just like determining relationship on a family tree, we can get an
idea about how closely related Dick and Harry are by counting the number of
mutations they share.
SIDEBAR: The letters at the beginning of SNP names are abbreviations
for the company, individual, project, or process that discovered them. For
example, BY3233 simply means it was the 3,233rd SNP discovered by Big Y
testing. DF83 was the 83rd SNP discovered by "DF," an
Now, ponder this SNP tree for Cooley group CF01 and related families:
Remember, each (or mutation) occurred in specific men at various
times in the past. "Upstream" SNPs emerged in men who lived further into
antiquity than did "downstream" SNPs. We know what SNPs these men possessed
because they were passed down to the present generation: we have them. They
can easily be sorted out into a tree by comparing test results of living
men. For example, looking at the above tree, I have SNPs
and everything above that
dating back more than 300,000 years. I share all but A7497 with the other
Cooley tester, YP4491 being our "parent" SNP (John Cooley of Stokes County,
NC). And we know that YP4253 is "his" parent SNP because the Cooleys share
it with the Hacketts—they do not have YP4491.
As mentioned above, we could give SNPs more human names. In the meantime,
we assign SNP names to forgotten souls much like we have with ancient skulls
that sit in museums and archives, tagged with alphanumeric identities. We
know the skulls but we don't know the men. We don't know the men in the
SNP trees, but we do know something of their archived DNA. To a
degree, we even know where these men (along with their SNPs) were born.