We started a discussion of the Thomas family which led us into some discussion of genetics. Gerry Parchman made two comments, which for the record, I feel should be entered into the Notes.
He felt, and I agree, that the reason that southwestern Pennsylvania became a center of attention of people living in Culpeper County, Virginia, was that soldiers in the French and Indian War became acquainted with the region. This seems very plausible and is a straightforward explanation.
Then Garry sent a comment to the list on genetics and the mechanism by which a new human life is created. I believe the following is essentially his words:
"As a biologist, I can't resist commenting on John's explanation of chromosomal "crossing over". His explanation was not quite accurate. When the two homologous (matching) chromosomes (non-Y) match up, during the sexual division process called meiosis, in order to generate the haploid gametes for fertilization, the chromosome pair can sometimes exchange one strand for another so that the resultant gametes (egg or sperm cells) have a new combination of genes on the chromosomes that are partly from the person's male parent and partly from the female parent. This "crossing over" occurs much more often than gene mutations, and allows for more genetic variation in offspring. For example if chromosome 18 received from one of a person's parents has gene mutations (alleles) called XYZ and the chromosome 18 received from the other parent has the gene mutation combination ABC, after the crossover event the chromosomes can segregate into the gametes as XYC and ABZ. This mixture is why most non-sex chromosomes cannot be used to trace ancestry. The male Y chromosome does not participate in this process with the X chromosome, so no crossovers can mix up the genes on the Y chromosome and it can be used to trace paternal ancestry. However, the X chromosome occurs twice in females and does undergo crossovers, so it cannot be used to trace female ancestry. Female ancestors are traced using the mitochondrial DNA, since all mitochondria have small amounts of their own DNA, and all mitochondria passed to the next generation come from the egg, not the sperm."
We appreciate this amplification. In the next Note, I will stick my neck out again and give you all a chance to comment.
(18 Apr 06)
We gratefully acknowledge the work of John Blankenbaker who published over 2,500 Germanna History Notes via the Germanna-L@rootsweb.com email list from 1997 to 2008. We are equally thankful to George Durman (Sgt. George) for hosting the list and republishing the notes via rootsweb.com.