Sex determination pathways evolve fast and can even be variable within species. Son et al. used the house fly as a model to study the evolution of sex determination because it has a male... Sex determination, the developmental process by which organismal sex is established, evolves fast, often due to changes in the master regulators at the top of the pathway. Additionally, in species with polygenic sex determination, multiple different master regulators segregate as polymorphisms. Understanding the forces that maintain polygenic sex determination can be informative of the factors that drive the evolution of sex determination. The house fly, Musca domestica, is a well-suited model to those ends because natural populations harbor male-determining loci on each of the six chromosomes and a biallelic female determiner. To investigate how natural selection maintains polygenic sex determination in the house fly, we assayed the phenotypic effects of proto-Y chromosomes by performing mRNA-sequencing experiments to measure gene expression in house fly males carrying different proto-Y chromosomes. We find that the proto-Y chromosomes have similar effects as a nonsex-determining autosome. In addition, we created sex-reversed males without any proto-Y chromosomes and they had nearly identical gene expression profiles as genotypic males. Therefore, the proto-Y chromosomes have a minor effect on male gene expression, consistent with previously described minimal X-Y sequence differences. Despite these minimal differences, we find evidence for a disproportionate effect of one proto-Y chromosome on male-biased expression, which could be partially responsible for fitness differences between males with different proto-Y chromosome genotypes. Therefore our results suggest that, if natural selection maintains polygenic sex determination in house fly via gene expression differences, the phenotypes under selection likely depend on a small number of genetic targets.

中文翻译：

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尽管有证据表明选择维持稳定的多基因性别决定，但原 Y 染色体对家蝇基因表达的影响很小。


性别决定途径进化得很快，甚至在物种内是可变的。儿子等人。使用家蝇作为模型来研究性别决定的进化，因为它具有雄性......路径。此外，在具有多基因性别决定的物种中，多个不同的主调节因子以多态性的形式分离。了解维持多基因性别决定的力量可以为推动性别决定进化的因素提供信息。家蝇（Musca Domestica）是达到这些目的的一个非常合适的模型，因为自然种群在六个染色体的每一个上都含有雄性决定基因座和一个双等位的雌性决定基因。为了研究自然选择如何维持家蝇的多基因性别决定，我们通过进行 mRNA 测序实验来测量携带不同原 Y 染色体的家蝇雄性的基因表达，从而分析了原 Y 染色体的表型效应。我们发现原 Y 染色体与非性别决定常染色体具有相似的作用。此外，我们还创造了没有任何原Y染色体的性别逆转雄性，它们的基因表达谱与基因型雄性几乎相同。因此，原 Y 染色体对雄性基因表达的影响较小，与之前描述的最小 XY 序列差异一致。尽管存在这些微小的差异，但我们发现了证据表明一条原 Y 染色体对男性偏向表达的影响不成比例，这可能是具有不同原 Y 染色体基因型的男性之间适应性差异的部分原因。 因此，我们的结果表明，如果自然选择通过基因表达差异维持家蝇的多基因性别决定，那么选择下的表型可能取决于少数遗传目标。