Well actually there is evidence that when you pick say myoglobin or some other
gene and use accumulated mutations to determine divergence of two species there is
a serious flaw. The premise that mutations occur in these two genes, in two different
organisms in two different genomic contexts, at the same rate is most likely wrong.
It is well established and being accepted finally that the genome is made of
many "domains" of which the accessibility to enzymes and oxidative agents etc
that might cause damage to the DNA and hence mutations differs. The accessibility
although not conclusively linked in all cases can reflect transcription status, time of
replication and/or rates of recombinaition. It is already known that transcription and
DNA repair (specifically Nucleotide Excision Repair) are intimately linked. Now if you
have domains with different transcriptional activity you can have different rates of
mutation that is reflected in efficiency of DNA repair.
So to make a long story short molecular clocks with such a basis are invariably inaccurate!
Graham Dellaire Snail Mail:
Red Cross, Research
McGill University Montreal Blood Services
Faculty of Medicine 3131 Sherbrooke St. East
Div. of Experimental Medicine Montreal, QC, Canada
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