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The explanatory power
of natural selection has been doubted since Darwin's day, and now molecular
biologist Gabriel Dover has introduced another force in evolution called
molecular drive in the book "Dear Mr Darwin"(2000). Mr. Dover
claims that organisms are "a product as much of the internal flux
of their genomes as of the external flux of the environment."
It all starts with the observation that repetitive DNA segments are homogenized
within a species. Many pieces of DNA exist in multiple copies in the genome.
For example the code for ribosomal RNA (the RNA required for gene transcription)
has 700 copies in humans. When multiple copies are examined between closely
related species it is discovered that a mutation in one copy will spread
throughout all the repeats even on different chromosomes in all the members
of a sexually reproducing population. The mechanisms for this spread are
apparently unequal crossing-over, gene conversion, and slippage.
Proteins and the regulatory regions of genes are modular, according to
Dover, and hence are prone to modification by the same mechanisms. These
regulatory regions, or "promoters" reside adjacent to a gene
and consist of modules which bind to the products of other genes, regulating
the initiation, tempo, timing and tissue specificity of the transcription
process of the adjacent gene.
What
it all boils down to is that changes are occurring within the genome without
the benefit of selection. In my presentation I will take a close look
at the mechanisms and implications of molecular drive.
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