Help me understand DNA testing

[ForresterModern]

Doctor in the house. Doctor hat on.

The Y chromosome, as stated above, is only present in males (with rare exceptions) and is passed directly from one's father to the son, generation after generation. Since names in the western european model present in england and scotland also passed the paternal surname from father to son (at least for the last few centuries), the name would follow the Y chromosome.

The Y chromosome is actually this pitifully small thing, with very limited genetic material included in small packets called genes, each gene with its own individual purpose. The chromosomes are made up of deoxyribonucleic acids (or DNA), which itself is made up of 4 chemicals known as nucleotides(cytosine-C, thymine-T, Guanine-G, and adenine-A) which are chemically strung together in a long linear strand. DNA is made up of two complimentary strands, as certain nucleotides mate up with certain other nucleotides across from one strand to the other. Certain sections of each DNA strand/chromosome code for specific protein manufacture which ends up causing a specific end effect like blue eyes or blond hair, when combined with the protein effects of the other matching chromosome (we have pairs of 22 different chromosomes plus either an XY mismatched pair in males or XX matched pair in females). Each gene also may have minor variations in its chemical makeup---for example a certain sequence of ACTG nucleotides in a certain location in a certain gene on a certain chromosome may code for blue eyes while a different sequence of nucleotides in the same place in the same gene on another similar chromosome would code for maybe green eyes. Since most chromosomes have nearly identical mates (pairs of same numbered chromosomes) the genes do battle to see what the eventual expression of those different genes will be (dominant, recessive, or codominance--in my example green (dominant) wins out over blue(recessive) and the individual will have green eyes).

Since the Y chromosome has little genetic material to match up with the much bigger X chromosome many x-related genes express the mother's contribution in outward appearence simply because there is not mate to contend with on the smaller Y. However the Y chromosome does still carry a significant number of genes which can be traced by biochemical tests, and those individual variations in nucleotide group ordering in those genes can be identified (variations similar to the blue eye-green eye discussion above) by the DNA testing everyone is talking about. Y chromosome genes rarely mutate spontaneously so they are a good marker to follow from one generation to the next, and so forth, in the paternal line. Multiple diferent variations for each geen exist, and multiple different genes can be tested and typed as to which variation is present in each gene. Males of similar lineage should have similar Y DNA chromosomal genetic markers, regardless of how many generations apart they might be.

So, for instance, 20 different males with the last name Macdonald all get DNA tested in Scotland, and we find that 4 of them have identical Y genetic profiles. We can say that they all descend from a common ancestor while the others do not descend from THAT ancestor, despite the MacDonald name. You may be an american MacDonald and get your DNA tested and it matches those four other MacDonalds, at some time in the past one of your paternal lineage was a MacDonald, and you share a common lineage with those other four MacDonalds, i.e., you are paternally related. Same thing even if your name is not now MacDonald---maybe you were a Macdonald who segregated into a sept subsequently taking the sept name instead of the paternally inherited name, maybe you or someone in your paternal lineage were adopted yielding a name change, maybe there was some illegitimacy in your past and a paternal line was started using your mother's name. Your Y chromosome genetic marker makeup will tell your paternal heritage as long as you have something to compare it to (the huge Y chromosome DNA database). The more genetic markers tested the more acurrate the matings are, so if you are really going to do it to try to trace ancestry backward into the "old country", wherever that may be, try to do as many markers as you can afford or are available at the time you do the test. More markers are being defined every month and the number of testable genes is increasing regularly (more than a hundred now I believe).

Doctor hat off. I have not been tested yet, but will be in the next couple years, once I narrow down my american ancestry back to the first Foster/Forrester who came to the US. Also waiting for the number of testable markers to go up, and hopefully the price to go down. This will help me find direct line descendants back in the old country, and hopefully some distant relatives, maybe even royalty (there is alledgedly at least one
knighted member of my lineage).


jeff