Saturday, October 24, 2015

Discussing DNA - As A Genealogist

At the cellular level, the human species functions under the directions of DNA.(1)  For each individual, this DNA is a unique combination of certain molecules passed down; half from father, and half from mother.  This combination is held within a specialized structure called a chromosome.(2) There are 23 pairs of these DNA carrying structures, resulting in 46 total individual chromosomes.  [22 pairs are called autosomes(3), and 1 pair is called germ cells, or sex chromosomes.  Some get all the fun!]  All lumped together, this is called the genetic material from which we all exist.

     The purpose of these chromosomes are to deliver a correct copy of itself to each daughter cell. When these copies are changed from their original form, they are called mutations.(4)  These mutations are permanent alterations that can be passed down the family tree, one generation to the next.  These changes can occur at a single site (point mutation), or involving the insertion or deletion of a number of genetic sites. (variable or multiple site mutation)  These changes, when recognized, have become "markers" among certain genetic groups that become a method of ethic identification. [haplogroups to haplotypes]

For the genealogist, the most important markers occur on 1) the Y-chromosome. [one of the sex chromosomes], 2) specialized DNA found in the ribosomes(5) of the mother in structures called mitochondria (6), and 3) on any other of those chromosomes called autosomes.

A series of drawings are shown which represent these concepts:

Y-chromosome DNA which is passed down from father to son on the "Y"  sex chromosome -

Squares and circles are drawn to represent the male [square], and female [circle].  The mutation found on this chromosome is a single [point mutation] called SNP - pronounced "snip".

Mitochrondrinal DNA is inherited through the maternal line.

This collection of DNA is relatively small but necessary for the energy production in all cells. [For those interested this is called oxidative phosphorylation.  Leave it up to all the moms of the world!]
The term is given as "mt-DNA" where "mt" stands for mitochrondrial.

Autosomal DNA are markers identified among the chromosomes that are not sex chromosomes.  They are passed down from the ancestors as a group of markers.  They are used to make generalized ethic determinations found among the families' prior generations.  This is generally expressed as a per cent of each marker that occurs among the family group.  It does not show a direct descent from their parents to their children, only distinct mutations that have occurred among family members of past generations.

 Whew...what a deal!

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(1) DNA = deoxyribonucleic acid [pronounced = dee-ox-e/ rye-bow/new-clee-ick ass-id] At least from my Kentucky twang!

(2) chromosome [pronounced = chrome-o-zone]

(3) autosomes = any chromosome other than a sex chromosome [pronounced = auto-zone (s) ]

(4) mutations = the process where changes occur in the number or structure of the genetic material

(5) ribosome = a structure outside the normal location of regular DNA (in the cytoplasm) that is responsible for protein synthesis.  This specialized DNA is found in the structure called the mitochrondria

(6) mitochrondria [pronounced = mito-condre-ah] = semi-autonomous organelle (in all cells) which produces the energy for life called oxidative phosphorylation [pronounced = oxy-date-ive  phos-for-a-la-tion]