Short Tandem Repeats (STRs)Conveniently for genealogists, men pass their Y chromosome and surname from father to son to son to son ... over the centuries. Their Y chromosome Short Tandem Repeat (STR) values (number of nucleotide repeats at each STR location) exhibit a unique genetic "signature" and are very stable. STRs do not mutate often. All the direct patrilineal sons and grandsons of a male will carry virtually the same Y chromosome, with only the occasional STR mutation occurring. In this way, a male's Y chromosome becomes a genetic ID tag for his surname lineage over centuries. That means that men who may not even know each other, but who share a common patrilineal ancestor some time in the past, will normally carry the same Y chromosome STR values passed down distant cousin lines. The STR markers that are tested help show, based on their unique mutation rates, matches to other males where the most recent common ancestor (MRCA) (the patrilineal male whom the matching lines branched off from) lived within a genealogical timeframe (since surnames came into use). The more STR values two men share, the more recently their MRCA lived. This is why we often test up to 67 or 111 markers: to confirm that the match is within a genealogical timeframe and to better estimate within how many generations the MRCA lived. So when a participant purchases an STR Y chromosome kit, they hope to identify matches in the database with distant cousins who share their surname. At that point they can exchange family information to help each other in their documentary research. STRs are what you see when you look at the "Y-DNA Results > Classic" page for our project at FTDNA. For a better look at the specific mutations that differentiate matches from one another within matching subgroups, try the "Y-DNA Results > Colorized" page. Non-Paternal EventsA non-paternal event (NPE) can occur before surnames were used, but we typically think of them within a genealogical timeframe. An NPE occurs when a Bowes wife—say Henrietta Bowes—conceived a son, either before or after marriage, by a male who was not a Bowes—say Jack Scanlon. Scanlon carried the Scanlon Y chromosome that belonged to his own surname, and voila, the little boy was raised among the Bowes as Hardly A. Bowes. Just kidding, he was still a Bowes for historical and family purposes, but he did have Scanlon's Y chromosome taking up just about 2% of his genome; and so, thereafter, did all his male Bowes descendants to whom he bequeathed it. Most of our participants are pretty confident when purchasing a kit that they don't have an NPE on their recent patrilineal line. You can expect an overall prevalence for NPEs of 2-3%. [1] Since our surname study includes people of the same name within a larger, historic surname group that's evolved over centuries, we inevitably find some NPEs within it. These are actually useful for identifying more recent matches one has within the larger surname group. (See DNA > Results Map - South of Ireland) [1] Engber, Daniel. "Who's Your Daddy," article. May 21, 2013. Slate. (URL: http://tinyurl.com/kf69er5; accessed 29 Jun 2013) |
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