I am curious to know if there is any known mechanism by which a
microbial line
of descent can eliminate sublethal mutations once they occur. In
sexually
reproducing popultations, independent segregation of chromosome
segments allows some genes to not be passed on. Also, those
recombinants containing the largest numbers of deffective genes are at
higher risk of genetic extinction than those with few. These
mechanisms allows sublethal mutations to be slowly decremented from
the population.
But, what happens in asexually reproducing organisms? My limited
reading on the
subject of conjugation (the microbial version of sex) does not suggest
a
comparable mechanism. If I understand correctly, when one cell inserts
some of
its chromosomal DNA into another, it retains its own copy. So there is
no loss by indepenndent segregation.
As I currently see it, each microbe stands at the end of an unbroken
line of
descent tracing back to its first ancestor. Along the way, multiple
donars may
have inserted additional DNA. All of its genes are said to have
arisen by a long series of mutations, filtered by naturally selective
processes. But beneficial mutations are considerably less frequent
than
deleterious ones. So, either A) Every living microbe comes from an
incredibly
LUCKY line of descent, receiving far more beneficial mutations than
detrimental
ones, or B) Sublethal mutations are flushed from lines of descent by
some
mechanism, or C) ...?
Thanks in advance for any insights or clarification you might offer.
Jim Pamplin
