Re: recombination question

I'll add a bit of additional comment on top of Perplexed in
Peoria's very excellent reply.

I suspect that, in the great majority of cases, no problem occurs
during crossover for the following reasons:

1. Many crossovers occur outside of of genes.

2. Oftentimes, as Perplexed pointed out, the difference between
two alleles is a difference of a single nucleotide base pair.
A crossover in the middle of such a gene is simply equivalent
to inheriting the allele containing the copied difference.

3. (This is more speculation on my part) Even when the crossover
produces an allele that is not found in either parent, the
result is not likely to result in a non-viable zygote. The
allele is composed of base pairs that do, in fact, work in
different forms in one or the other of the parents. The new
version is novel, but probably not deadly.

Whether it confers an evolutionary advantage, a disadvantage,
or neither one, is a matter of chance. This is part of the
stuff of variation that natural selection works on.

There are documented cases of more serious crossover errors that
still result in viable and even advantages outcomes. I'm
thinking of cases where the "chiasma", i.e., the point where the
crossover occurs, is different on each chromosome so that a whole
gene can be added (i.e., one copy from the mother and one from
the father) to one chromosome and both copies deleted from the
homologous chromosome. I know this has been found in some
plants.

Alan


.

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