性染色体起源于常染色体，现有的假说认为为了保证性别决定和性别对抗基因稳定连锁在某一条性染色体上而不进入对立性别，性染色体之间重组被抑制，最终导致了Y或者W染色体的退化。如果该演化模型成立，将预期性选择越强烈的物种，XY之间或者ZW之间差异将越大。本项目将通过基因组学的方法，以鸟类为模型，在重构至少30种近缘鸟类物种性染色体基因组演化历史的精细图的同时，检验它们的ZW染色体差异度是否与它们的两性表型差异直接相关。这一关联性将为性染色体演化的一般模型首次提供大规模的实验证据。其次，本项目将通过比较W染色体和Y染色体的相对突变速率，进一步量化地探讨为何鸟类的ZW染色体要比哺乳类的XY染色体分歧地慢。最后，我们将通过获得的大量的鸟类W染色体的序列，鉴定出通用的鸟类性别特异分子标记和可能的性别决定基因和调控区。

Sex chromosomes originated from autosomes, and have suppressed homologous recombination due to the selection for linkage between the sex-determining genes and sexual antagonistic genes. The loss of recombination restricted both types of genes from being inherited in the opposite sex, and also leads to the degeneration of Y or W chromosomes. If this model holds, it is expected that species undergoing stronger sexual selection would diverge more between their X/Y or Z/W chromosomes. This project aims to test this model by reconstructing the fine evolution history of at least 30 related bird species, and inferring whether their phenotypic sexual dimorphism is correlated with their Z/W genomic sequence divergence level. Such a correlation provides experimental evidence for the general model of sex chromosome evolution for the first time. We are also going to quantitatively compare the relative mutation rates of W vs. Y chromosomes, in order to explain why birds’ ZW chromosomes generally seem to diverge much slower than mammals’ XY. Finally, we are going to identify universal molecular markers for sexing the bird species and potential sex-determining regions based on the studied species’ conserved W-linked sequences.