BACKTRACKING

Backtracking the Y-Chromosome

by Terry Hogan

In the March 1, 2007 issue of The Zephyr, I had an article appear that was titled Genetic Genealogy. The short version of that article was that I had sent a sample of my DNA for the Y-chromosome to be analyzed at 37 loci. These data would then be compared with other Y-chromosome data provided by other genealogists, to find out who I was closely related to, based on the tests results of the Y-chromosome.

Why the Y-Chromosome? To answer, I need to explain a little genetics that you may remember from school days. Women are women because they have two X-chromosomes. Men are men because they have an X-chromosome and a Y-chromosome. Because there are two X-chromosomes in women, the chromosomes can "trade" a little genetic material between the two chromosomes. This exchange of genetic information between the two X's is called "translocation". It helps create a little greater genetic diversity by stirring the pot. In evolution, that is probably good. For tracking ancestors, that is bad.

Males have only the one X and the one Y chromosome and thus cannot trade genetic material between the two chromosomes. So the genetic material stays pretty much the same on the Y-chromosome, except for mutations. As there is only one Y-chromosome and that is what makes an offspring a make, fathers pass on the Y-chromosome from father to son, generation after generation, with little variability.

This consistent Y-chromosome thus becomes a "traceable" characteristic from son to father, to grandfather, etc. So, males can have their Y-chromosome analyzed and compared with others to determine likely shared common ancestors. The closer the match of the data from the Y-chromosome, the higher the statistically probability that the two males are related. Similarly, the closer the match, the more likely that the two shared a common ancestor recently.

Alas, females cannot do this testing as they lack a Y-chromosome. So females must impose on a male blood relative such as a father or uncle to give up a little DNA. Of course there are also some risks. Unknown adoptions or family infidelity might show up, particularly if two male members of a family each submit DNA independently. Two brothers should have a very high probability of a perfect match. If not, it could be a lab error or the start of a new family history.

But so much for the background and "genetics 101". If Dr. Billy Gear, who taught me several genetic courses while I attended Knox College many years ago, reads this article, I hope he will “cut me some slack”. What we are doing now wasn't even vaguely a “gleam in anybody's eye” in the mid-1960’s.

Anyway, I got my Y-chromosome data back from "Family Tree DNA", an organization that does this type of work and is the lab of choice for the Hogan DNA project on the Internet. My Y-chromosome matched 36 out of 37 loci for the family group of Hogan’s that I believe were "mine" based on about 20 years of circumstantial data collection. According to the going rate, a match of 36 out of 37 would get you about a 90% probability that the most recent common relative would have occurred within 8 generations. If it had been a 37 of 37 (perfect match), it would have given about a 90% probability in 5 generations.

The test results for my Y-chromosome are compared with chromosome data from family group members whose lineage is proven beyond reasonable doubt. When mine matches with a high degree, it doesn't tell me "who" the common ancestor is or "how" the relationship tracked down to me. It just says, on a probability basis, that it is very likely that a family relationship is present. But it was my traditional genealogical researches that led me to believe I could predict the association that in fact was shown.

And no, the lab did not know who I thought I was related to. The lab doesn't care. It makes money off the test and running a computer for the data comparison. So, the test can be thought of as one more very strong, but still circumstantial piece of evidence. But it is good enough for me.

As such, I'm pretty satisfied that my known great grandfather, Jasper Newton Hogan, was indeed the son of Banister W. Hogan, who was born in Montgomery County, North Carolina. Both fought in the Civil War. Jasper fought with the 91st Illinois Infantry from 1862 through the end of the war in 1865. Banister joined a North Carolina unit and died in a hospital in North Carolina less than a year later. It was another case of father against son in the American Civil War.

If you might be interested in the genetic research, a good place to start is the Internet. Do a "Goggle" or similar search with your surname of interest and add "DNA" with the search. See if you can find someone who is already hosting a surname database. Getting DNA test results with nobody to compare with won't help you much.

If you are interested in seeing the Hogan DNA project, you can go to www.worldfamilies.net/surnames/h/hogan/results.html. I'm guessing you could drop the "h/hogan/" and insert the appropriate initial and surname of interest to see if you might find something of more specific interest to you. It might be worth a try.

Y-chromosome? Y-not.

3-14-07