In the first of my present round of posts, I described the difference between Y-STRs and Y-SNPs. I'll start with a brief review. Some definitions:
SNPs and STRs exist throughout the genome. The mutations we find in mitochondrial DNA are SNPs. We see the terms often preceded by "Y-" simply to denote that we're talking about mutations on the Y chromosome, which is about all I've talked about in the last several posts.
STRs tend to be fickle. The count can fluctuate—up or
down—from one generation to the next. Yet they are considered to be
stable enough that general predictions can be made about relationships
between two individuals going back approximately fifteen generations.
That's not to say that precise predictions can be made, just enough that
test results can be grouped together, especially when the surnames are the
same. The comparisons become more significant when geographic regions and
eras are also equivalent. Given that, I was surprised that the Hackett
Y-STR match to the
SNPs are not so fickle. Once a mutation appears (a T flipped to a G, for example), it's passed down from one generation to the next unchanged. Stable SNPs have been found that are over 300,000 years old. With these, we can make much better predictions, such as the case with the Hacketts and Cooleys—from a highly nebulous relationship to one that some kind of year can be attached, even if approximate. But it would be a mistake to throw out STRs once we have advanced SNP testing done. Both are important pieces of data and can be used in tandem to gain a fuller picture.
There are three CF01 Cooley testers who are undoubtedly related but don't
fit in the tree of John Cooley (c1738-1811) of Stokes County, NC, even
though one bio says the family had origins in North Carolina. So far, the
line doesn't appear on the radar until the birth of William Henry Cooley in
1797 and of James Cooley in 1808 or '09, both born somewhere in
Pennsylvania. They were of the right age to have been grandchildren of
John's but we can place none of his sons in Pennsylvania. Besides, each of
the three descendants have two Y-STR markers that are not found among the
Stokes County Cooleys: DYS464b has 15 repeats (as does the Hackett tester,
which means that it is relatively old) and
I've mapped both SNPs and STRs in this graphic, arranging them according
to their relative ages. The "other" Cooleys appear down the far left arm.
Not enough data is known to determine the order in which the
We can also throw