February 15, 2015

IMPORTANT: Please Check with Us before Ordering ANY Y-DNA or mtDNA Tests!

"Big Y" SNP Test Now Available

An Important Note on Clade and SNP Testing

Overview

Y-chromosome DNA contains two different types of genetic markers. The first, known as a short tandem repeat or STR, is the type tested in a member's initial order (the 12-, 25-, 37-, 67- or 111-marker Y-DNA test). STRs change relatively often (from a genetic perspective); consequently, if two men match very closely on a high number of markers (90% or better on 37 or more markers), the results indicate a very high likelihood that they are related within 24 generations, or approximately 600 years. This is significant because most surnames in Western Europe arose within this time frame. STRs are therefore used to match men who belong to the same family line.

STRs are extremely valuable in determining genetic distance because it is possible not only to determine whether or not two men match on a particular marker, but also how distant they are when they do not match. For example, if one man has a value of 13 on a particular genetic marker, and another has a value of 15 on the same marker, they are then separated by a genetic distance of 2. (By contrast, with mitochondrial DNA, all that can be said is that the values do or do not match; it is not possible to calculate genetic distance.)

Thus, the STR may be thought of as roughly equivalent to a genetic fingerprint or signature for a man's family line, at least when higher numbers of markers are involved. This string of marker values is what is known in genetic genealogy as a haplotype. In looking at the Windsor Project results, for example, there are four distinct STR haplotypes (excluding the Unaffiliated category), all of which represent distinct family lines.

The second type of genetic marker is known as a single nucleotide polymorphism or SNP (usually pronounced "snip"). SNPs change or appear only infrequently, perhaps every 2000 years or so. Consequently, they allow men to trace their deep ancestral roots by establishing the genetic tribe or haplogroup to which they belong. If two men belong to the same haplogroup, they may be related; if not, they cannot be related within the 24-generation limit mentioned above.

In recent months, SNP research has been advancing rapidly. It is now possible to classify men into a much larger number of clades and subclades (genetic jargon for groups and subgroups within a haplogroup). As the knowledge gained from this research accelerates, it may become possible to identify individual men within a family by their unique haplogroup designation. For this reason, if nothing else, the Windsor Project strongly recommends that members have their respective haplogroups confirmed through clade testing; however, please check with us before you have ANY such testing done!

If you test only STRs, you are effectively testing only half of your Y-DNA.



British Y-DNA Haplogroups

At present, genetic genealogy recognizes 20 Y-DNA haplogroups the world over, designated A through T respectively. Of these, only about four or five occur with any great frequency in the British Isles.

For an extensive discussion of any or all of these, the reader is directed to the relevant parts of the Eupedia website at www.eupedia.org, or to the various articles on Wikipedia. Family Tree DNA also maintains a number of Y-DNA haplogroup projects that provide a great deal of valuable information. It should be noted that the Eupedia articles, although informative, are probably somewhat dated and in need of revision.

By far the largest Y-DNA haplogroup in the British Isles is R1b. This haplogroup is strongest along the Atlantic coast 79% of the male population of Ireland and 84% of the male population of Wales), falling slightly to 73% in Scotland and 67% in England. This huge genetic "tribe" has experienced a great number of mutations, with the result that there are several important subclades. Two very common ones in the British Isles are the "Ibero-Atlantic" subclade, defined by the presence of SNP marker L21, and the "Germanic-Frisian" subclade, defined by the presence of SNP marker U106.

The next most prevalent Y-DNA haplgroup in the British Isles, although a distant second, is I1, a heavily Scandinavian haplogroup which is normally divided into Anglo-Saxon and Norse subclusters. A result of "8" at STR marker DYS455 is almost a dead ringer for membership in this haplogroup, as nearly all men who belong to I1 have this result, and as it is rare elsewhere. A result of "9" at DYS511 and a result of "12" at DYS462 are considered "Anglo-Saxon," whereas results of "10" and "13" on these two markers respectively are considered to be "Norse."

Until recently, little was known about I1 subclades, and a large number of men in this haplogroup simply had to content themselves with being "generic." However, within the last year a number of heretofore-unknown SNP markers have been discovered, the most important of them being Z58, the defining marker for I1a3, and Z63, the defining marker for I1a4. If you belong to Haplogroup I1 and you have not tested for either of these markers, please get in touch with us.