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shigeta
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This is a little tricky.

First of all lets be clear about 'bringing together favorable alleles' (or any alleles) represented by site mutations on 2 chromosomes:

--------A------------------
             X     
------------------B--------

If the two dashed lines are two copies of the same chromosome, then a recombination event at X may produce:

--------A---------B--------

Allowing both A and B to be passed along to offspring. Any given case of recombination might actually harm resulting offspring. But in cases where A and B together are beneficial, over the course of generations you will find AB genotype combinations show up more frequently in the population because of selection and competition.

So its not just recombination, but recombination and selection which create favourable combinations of alleles in populations.

But consider a simple case where recombination does not come in. You may have an A genotype and then wait for B to show up by random mutation. That would take perhaps thousands or even millions of generations before such a thing happens at random. Recombination is a powerful accelerator of evolution.

shigeta
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