Department of Zoology & Biodiversity Research Centre, University of British Columbia, Vancouver, BC, Canada, V6T 1Z4.
New Phytol. 2019 Nov;224(3):1241-1251. doi: 10.1111/nph.16083. Epub 2019 Aug 24.
Differentiated sex chromosomes are thought to develop through the accumulation of polymorphisms at loci subject to opposing selection between males and females, and/or between haploids and diploids. As sex chromosomes differentiate, reduced recombination becomes favored between selected loci and the sex-determining region, strengthening genetic associations between alleles favored in a sex and the corresponding sex chromosome. Here a model is analyzed to explore whether polymorphism at one sexually or ploidally antagonistic locus facilitates the spread of rare alleles at other loci experiencing antagonistic selection, promoting further differentiation of the sex chromosomes. It is found that antagonistic polymorphisms can spread and capture other such loci, building 'genomic islands' of differentiation on sex chromosomes, but the conditions are very restrictive, requiring the loci to be strongly selected, tightly linked and distant from the sex-determining region. Epistatic interactions can facilitate the promotion of polymorphism among selected loci, but only if preferentially favoring heterozygotes. Although these results apply to any taxa, plants provide a fertile ground for testing these and related theories given the recurrent evolutionary transitions to dioecy, which provide multiple opportunities to track the early evolution of sex chromosomes.
性染色体被认为是通过在雄性和雌性之间、或在单倍体和二倍体之间受到相反选择的基因座上积累多态性而发展起来的。随着性染色体的分化，选择基因座和性别决定区域之间的重组减少，从而加强了在一个性别中有利的等位基因与相应性染色体之间的遗传关联。本文分析了一个模型，以探讨一个性或倍性拮抗基因座上的多态性是否有助于其他经历拮抗选择的基因座上稀有等位基因的传播，从而促进性染色体的进一步分化。结果发现，拮抗多态性可以传播并捕获其他此类基因座，在性染色体上形成“分化的基因组岛”，但条件非常严格，需要基因座受到强烈选择、紧密连锁且远离性别决定区域。上位性相互作用可以促进选择基因座之间的多态性，但前提是优先有利于杂合子。尽管这些结果适用于任何分类群，但植物为检验这些和相关理论提供了肥沃的土壤，因为植物多次发生雌雄异株的进化转变，这为追踪性染色体的早期进化提供了多次机会。
