Michael Cooley's Genetic Genealogy Blog GEN • GEN
1 September 2019

Brief Cooley CF09 Redux

Cooley Group CF09 has had four Big Y testers. Ten to fifteen million positions on their Y chromosomes have been tested. (Y-DNA markers are inherited as virtual clones from their father-lines.) Together, they comprise a Y-DNA haplogroup known as R1b-SK411, which is the name for a simple DNA marker: position 13302299 on the Y chromosome mutated from the usual G to an A. In fact, of those millions of markers tested, the four testers vary from one another by only a handful, as shown below. The Earliest Known Ancestors (EKAs) names in this diagram all resided in North Carolina.




The two grayed out markers exist in non-stable regions of the Y chromosome and, therefore, can't be verified with Sanger testing (such as that provided by YSEQ). Therefore, I'm leaving them out in the following analysis.

Kit #252522, the descendant of Woodijah, is not a Big Y tester. He tested the five SNPs (the name for this kind of marker) discovered by the Big Y of his distant cousin (via James Cooley, 1758-1834) and is positive for only two of them.1 This is great news because we now have two genetically-verifiable branches from James, which is the aim of these tests: verify the genealogical branches of a tree by genetic testing. These two SNPs, then, constitute a very specific Y-print that James Cooley was born with. It's unknown whether #252522 has any private (unmatched) SNPs; it will require a Big Y to discover their presence. Therefore, he's not included in the following calculations.

We don't know, and may never know, who the common CF09 ancestor was. But we do know that he was born with the seven markers in haplogroup R1b-SK411. In fact, we might as well call him SK411. His ongoing male progeny have, and always will have, those markers. Anyone who has some but not all of them will be of a collateral branch, just as we've proven that #252522 and #B12855 are collateral to one another. (We already knew that through the genealogy. Genetics proved it.)

Each of the four testers has markers not shared with one another, listed left to right, six, three, five, and two — sixteen in total. They emerged in their respective lineages through the generations following the SK411 ancestor. Markers of this sort, known as Single Nucleotide Polymorphisms (SNPs), are believed to occur at an average of one every 144 years. But because we're talking biology and not mathematics, their manifestations are random and cannot be predicted. Still, we can determine a bare statistical analysis by counting all the mutations descended from SK411, then divide by the number of testers, and multiply by 144. In other words,


Sixteen SNPs, divided by four testers, multiplied by 144 years
(16/4) * 144 = 576 years


That's a long time ago, but it's imprecise. Nevertheless, it serves as a benchmark for now. Obviously, more descendant markers will provide a more accurate set of probabilities. It should be noted, however, that the only tests available for SNP discovery are expensive. FTDNA's Big Y looks at up to fifteen million markers but costs several hundred dollars. YSEQ's Whole Genome Sequence is even more expensive.

So, we've given the testers' Most Recent Common Ancestor (MRCA) a temporary name, SK411, and a very iffy timeframe. Still, the man's Y-DNA profile is known, and with that we can spot his descendants and reasonably close relatives. In time, once testing from collateral lineages arrive, we can begin to see when the seven SK411 markers emerged among the MRCA antecedents.

How does everyone fit on this tree? Obviously, those with the name Roach who are positive for SK411 can test the six markers descended from James Roach. If someone else in the CF09 group suspects they're closer related to Washington Coley than to Benjamin Coley, we have markers you can test.

Individual SNP testing can be done at FTDNA for $39. YSEQ will test them for $18, although a new kit will be needed — and I recommend doing that for anyone who doubts they can ever afford the Big Y. Yes, that test is desirable for SNP discovery, but the Sanger test at YSEQ is a good alternative, kit #252522 being a good case in point.

As always, I'm available for questions.

1 SNP is the acronym for a Single Nucleotide Polymorphism, a term that is actually very descriptive: Nucleotides, also known as a bases, are the genetic letters of virtually every living thing (A, C, T, and G). A SNP occurs when a single letter has "morphed" into one of the other letters; for example, a T to a G. These are very useful when they occur in stable regions of the Y chromosome. Such SNPs are known to have passed from one generation to the next for more than 300,000 years. Of course, new ones emerge every few generations. This can be imagined with a strong of beads. New beads are added (or changed) now and again and the string passed down to all subsequent males.