Effect of recombination on the rate of loss of genetic variation

Question

Following up from this question: Does recombination increase the additive genetic variance for fitness?

(I'm thinking about the evolution of additive genetic variance and differences between the sex chromosomes and autosomes. Assume males are heterogametic (XY) and females XX, recombination occurs on the X in females, but not between X and Y in males. This means X chromosomes recombine at 2/3rds the rate of autosomes. Answers need not necessarily relate to sex chromosomes as many other factors should be affecting their evolution and additive genetic variance)

As far as I can tell, recombination should improve the efficiency of selection as variance in fitness of the population of chromosomes increases (because favourable mutations can combine more easily and deleterious ones do too) which should in turn reduce additive genetic variance (right?). But then recombination means many more combinations occurs which means additive genetic variance might be higher.

So, if I sample the additive genetic variance in a trait in a population where chromosomes that do recombine and a population where chromosomes do not recombine, where should we see the most variance (the recombiners or non-recombiners)?

Answer 1

I found a key paper for myself from an issue of Nature Reviews Genetics last year. It discusses and reviews how recombination affects the rate of genetic variation at the sequence level.

A key concept is that of selective interference, which is what I had stumbled across in the question, this is when the efficacy of selection is reduced because "recombination fails to break down linkage disequilibrium at selected loci." Simply, a beneficial mutation in a system of no recombination is only as fit as the background it is in, if recombination is extremely high (no LD whatsover) then the fitness is defined only by it's own effects. This means that recombination can reduce polymorphism because selective interference will reduce the speed at which non-neutral alleles are fixed or lost.

However, recombination maintains polymorphism, because without it there is a greater potential for hard sweeps, soft sweeps, partial sweeps, and background selection to all remove genetic variance. For sweeps a beneficial mutation will drag any mutations it is linked with to fixation, the further from the allele the weaker that effect is.

It seems that over riding effect of recombination is to maintain genetic variance despite the increased rate at which an mutation can fix when there is no selective interference because it reduces the polymorphism reducing effects of sweeps and background selection.

"It is expected that neutral genetic variation will be systematically depleted in genomic regions with little recombination."