Shaking the Family Tree by Buzzy Jackson

Author:Buzzy Jackson
Language: eng
Format: epub
Publisher: A Touchstone Book
Published: 2010-07-15T00:00:00+00:00

Chromosomes

DNA is a molecule. This molecule contains a person’s (or any organism’s, but we’ll stick to humans here) complete genetic code. Most of that genetic material lives in the nucleus of each cell in the form of chromosomes: twenty-two pairs of chromosomes and two chromosomes that determine sex—arranged as XX for women and XY for men. When the male’s sperm, which has twenty-three unpaired chromosomes, fertilizes the female’s egg with its twenty-three unpaired chromosomes, their DNA pairs up to form twenty-two new pairs plus the XX or XY pair. The result of this combination is a single cell containing genetic information from both the father and mother, and this unique cell begins to replicate itself, eventually growing into an embryo, a fetus, and ultimately into an infant human being. 1 That would be you. And me.

Geneticists have identified (and continue to identify) genetic markers, which are segments of DNA located in places along the DNA sequence that correspond to heritable traits such as blue eye color or hemophilia. Markers are present in all DNA, and one of the easiest places to test for them is in the DNA present in the Y chromosome, which is passed exclusively from father to son (because women do not possess a Y chromosome). There are four types of inherited DNA: Y chromosome, mitochondrial DNA, autosomal DNA, and X chromosome. Only the first two factor into most genealogical DNA tests, though, so we’ll focus on those.

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