There are two ways to test the Y-chromosome. The basic, more common test is called STR (Short Tandem Repeat) and results in the series of marker values with which most of us are familiar. Tests range from 12 to 67 markers, with 100 marker tests soon expected. Each person’s set of marker values is called his haplotype
There is another way to test the Y-chromosome called SNP (Single Nucleotide Polymorphism), which is used to confirm one’s haplogroup. A haplogroup consists of all those haplotypes whose ancestry converges on one person, usually a person who lived thousands of years ago. People of different haplogroups cannot be related. Another name for a SNP test is a “deep clade” test.
Both tests depend on mutations. Markers (STRs) mutate much more rapidly and are used to determine modern relationships, especially among persons sharing the same or similar surnames. They are most valuable in determining a common ancestor who lived since surnames were adopted (usually about 1200 AD). SNP mutations occur rarely and therefore are “deep ancestry.” In our project, we have two major haplogroups—R and I—that first separated perhaps ten thousand years ago, and these have evolved into three sub-haplogroups (or sub-clades)—R1b, I1a, and I1c. Researchers currently are working on these to divide them even further and to associate them with geographical origins. And that basically is their value.
For example, the sub-clade R1b1c7 has been determined to be Northwest Ireland/Southwest Scotland. It is believed to have appeared some 3500 years ago, so anyone thus classified knows that his Y-chromosome line goes back that far to that area. Certain Scots, Frisian, and Nordic sub-clades also have been identified, but there are many others still to be pinned down. However, many will be, and soon.
The testing companies usually can estimate one’s haplogroup from the haplotype (markers), but only a SNP test provides positive identification. The cost is reasonable—FTDNA charges $79—and the identified haplogroup is placed on project websites so that all researchers can make use of it. There is further explanation of Deep Clade Tests on FTDNA’s website at http://www.familytreedna.com/. The test can be ordered via one’s FTDNA Personal Page.