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Archiver > GENEALOGY-DNA > 2000-11 > 0974035279
From:
Subject: Re: [DNA] Scott Woodward at Saint Marys County, MD event
Date: Sun, 12 Nov 2000 08:21:19 EST
In a message dated 11/11/00 7:05:26 PM Pacific Standard Time,
writes:
> but surely there is more DNA than just the two lines??
Yes, indeed. The entire human genome has 23 chromosome pairs in the cell
nucleus. It is 3 billion "bases" in length. Bases are the chemical units that
string together to form the code, abbreviated A for adenine, T for thymine, G
for guanine, and C for cytosine. The Y chromosome only has about 60 million
bases and the mtDNA outside the nucleus only has 16K (although there are many
copies in each cell).
The reason we place so much emphasis on Y chromosome and mtDNA testing here
is that you know with certainty where you got your Y chromsome and your
mtDNA. For your other chromosomes, you know you got one of the pair from your
father and the other from your mother. But you don't know whether the one
your father gave you came from HIS father or HIS mother. For an additional
complication, chromosomes can swap parts -- this is called "crossing over."
This means the chromosome your father gave you could be 2/3 from your
paternal grandfather and 1/3 from your paternal grandmother.
All of this makes tracing relationships very fuzzy, which is why I posed my
question for Scott Woodward re the utility of collecting four generation
pedigree charts.
If you can find a high school or college biology text, you could follow the
diagrams better than my explanation, I'm sure. Which reminds me, back when I
was in high school, we didn't even know how many chromosomes there were! I
was taught that we have 48.
Ann Turner
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