![]() Phasing allows us to date the suppression of recombination on the sex chromosome and provides unprecedented resolution to identify sexually antagonistic selection in the recombining region of the chromosome. Here we perform an analysis of phased young sex chromosomes to look for signals of sexually antagonistic selection in the Japan Sea stickleback ( Gasterosteus nipponicus ). This form of selection is thought to be key to the evolution of sex chromosomes but is hard to detect. Intralocus sexually antagonistic selection occurs when an allele is beneficial to one sex but detrimental to the other. Here, we model a simple and testable hypothesis explaining the stepwise extensions of recombination suppression on sex chromosomes, mating-type chromosomes, and supergenes in general. This may explain why sex chromosomes remain homomorphic in some organisms but are highly divergent in others. However, inversions capturing a permanently heterozygous allele were found to be less likely to spread when the mutation load segregating in populations was lower (e.g., under large effective population sizes or low mutation rates). Similar results were obtained with models assuming recombination-suppressing mechanisms other than chromosomal inversions and for supergenes other than sex chromosomes, including those without XY-like asymmetry, such as fungal mating-type chromosomes. Permanently heterozygous alleles, such as the male-determining allele in XY systems, protect linked chromosomal inversions against the expression of their recessive mutation load, leading to the successive accumulation of inversions around these alleles without antagonistic selection. We show here, by mathematical modeling and stochastic simulation, that recombination suppression on sex chromosomes and around supergenes can expand under a wide range of parameter values simply because it shelters recessive deleterious mutations, which are ubiquitous in genomes. However, it has proved difficult to obtain empirical evidence of a role for sexually antagonistic selection in extending recombination suppression, and antagonistic selection has been shown to be unlikely to account for the evolutionary strata observed on fungal mating-type chromosomes. The reasons for this remain poorly understood, but the principal hypotheses proposed to date are based on antagonistic selection due to differences between sexes. With AfterPay, there's no waiting and we'll ship out your order immediately as normal.Many organisms have sex chromosomes with large nonrecombining regions that have expanded stepwise, generating "evolutionary strata" of differentiation. *If you fail to have sufficient funds available for AfterPay to automatically deduct payment on due instalment dates you will be charged a late fee of $10, and if the instalment payment remains overdue, an additional $7 will be charged one week later. If you wish to return your goods you can choose to receive an exchange, or the Afterpay payment plan can be cancelled before the first payment at no charge. First time AfterPay buyers will need to make the first instalment payment at the time of their purchase. Enter your details with Afterpay and you're done.Īpproved AfterPay buyers will require the funds for the first payment to be available on their card at time of checkout, however the first payment won't be deducted for 14 days.On the checkout page select Afterpay as your payment method. ![]() ![]() Add your items to your shopping bag, and checkout as normal.
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