GENEALOGY-DNA-L ArchivesArchiver > GENEALOGY-DNA > 2002-09 > 1032352099
Subject: Re: [DNA] query about looks being different than dna
Date: Wed, 18 Sep 2002 08:28:19 EDT
In a message dated 09/17/02 11:54:01 PM Pacific Daylight Time,
> What would be the explanation of looks being different than what DNA shows?
The genealogical DNA tests trace either your straight paternal line or your
straight maternal line, only a tiny fraction of your total ancestry.
Furthermore, the tests use non-coding areas of the Y chromosome or mtDNA,
sometimes called "junk" DNA, so they have no direct influence on any physical
However, the Y chromosome and mtDNA are inherited as a unit, so the "junk"
and coding areas (genes) do travel together. What sorts of genes are on the Y
chromosome and mtDNA?
The Y chromosome is very small to start with (less than 60 million bases out
of the 3 billion total). It has not been completely sequenced because it
contains a large amount of very repetitive "junk." The coding areas have
probably all been sequenced, but they involve a small number of genes, the
major one being called SRY, or sex-determining region Y. This gene determines
maleness by causing the primitive gonadal tissue in embryos to differentiate
into testes instead of ovaries. That in turn initiates a cascade of events as
the testes start producing testosterone. Other genes on the Y chromosome are
involved in sperm production and so forth, but as far as I know, there are no
genes on the Y chromosome which influence the physical traits which we
associate with various geographic origins.
Mitochondrial DNA is likewise exceedingly small (16,569 bases long), and the
genes code for enzymes involved in energy metabolism. This is an absolutely
vital function, and there are many mitochondrial diseases, with symptoms
depending on which tissues have accumulated enough defective mitochondria to
cause energy production to plummet below a certain threshold. But again, this
is unrelated to visible physical traits such as eye color.
PubMed has a nice collection of textbooks which you can search by key word
for more information:
You can see what genes are on the Y chromosome and mtDNA at
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