Mutation is indeed influenced by environmental factors but I don't know
enough about the molecular clocks used by evolution scientists to explain
how this factors into their model. However, I can say that environmental
factors would have a greater impact on mutation rates in simple organisms,
especially those that are unicellular. Mammals, on the other hand, have
sophisticated DNA repair systems, detoxification systems, and physical
barriers (hair, integument) that help minimize the effect of environmental
mutagens.
>Obviously, there are some exceptions to this and immunogenetics may be one
>of them (help me out here, Steve).
The lesson from the MHC system is that different genetic regions may have
different intrinsic mutation rates. This brings into play the different
mechanisms that can account for mutation, such as gene conversion which play
an important role in creating great heterogeneity in the MHC genes of many
(not all) species. However, this point gets to the issue of how one
"calibrates" the genetic clock. I would guess that such calibration has to
be done for each loci examined. An interesting sidline: a couple of years
ago I saw a poster at a meeting which concluded from such molecular studies,
that HIV (the AIDS virus) is about 10,000 years old.
Steve
____________________________________________________________________________
Steven S. Clark, Ph.D. Phone: (608) 263-9137
Associate Professor FAX: (608) 263-4226
Dept. of Human Oncology and email: ssclark@facstaff.wisc.edu
UW Comprehensive Cancer Ctr
University of Wisconsin "To disdain philosophy is really to
Madison, WI 53792 be a philosopher." Blaise Pascal
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