molecular drive explained!

Joe Felsenstein joe at GENETICS.WASHINGTON.EDU
Sat Nov 23 02:26:38 EST 1991

In his reply to my posting Gabriel Dover discusses molecular drive and why he
feels it is a useful term.  I continue to disagree.  On one point I readily
concede: "concerted evolution" is the description of the phenomenon, and I
should not have used it as the name of the mechanism.  The mechanisms involved
      gene conversion (biased or unbiased, intra- or interchromosomal)
      unequal crossing-over within a tandem family
      genetic drift
The first two are the critical ones which spread mutations through the
family of repeated sequences and result in the evolution being "concerted".

All of these are forces were recognized for years before the term "molecular
drive" was suggested.  Is there a utility in the term?  The term "drive"
suggests to the listener that it is a force for rapid change, emanating
from intrinsic "molecular" forces.  Certainly there are such (biased
gene conversion).  But homogenization of gene families may also occur
because of unbiased gene conversion, or, if they are tandem families,
by unequal crossing-over.  In the unbiased conversion or unequal
crossing-over case the net rate of evolution is not increased, and it
was to point that out that I gave as an example this case (which
certainly is a case of concerted evolution if population size is finite).
If "molecular drive" is the name for the process(es) that explain
concerted evolution then it would seem to apply to this case too.  And
in this case the term "drive" is particularly unfelicitous.

The above mechanisms having already been known, and under active investigation
as explanations for concerted evolution, it seems of no utility to declare
the discovery of a new evolutionary force which consists of these forces.

Joe Felsenstein, Dept. of Genetics, Univ. of Washington, Seattle, WA 98195
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