AbstractsBiology & Animal Science

The young Y chromosome in papaya provides a good model to study the evolutionary tempo of Y chromosome degradation. In this study, comparative genetic analyses of 70 X-Y gene pairs showed that Y-linked genes have significantly more deleterious mutations than X-linked genes, suggesting the degeneration on the Y. However, this asymmetric evolutionary pattern is only confined to the oldest stratum, indicating a relatively slow degeneration tempo of the papaya Y chromosome compared to neo-sex chromosomes in Drosophila. Population genetic analyses based on protein-coding sequence variation of six X-Y gene pairs on the oldest stratum also identified elevated nonsynonymous polymorphisms and reduced codon bias on the target X region relative to the neutrally evolving autosomal regions. This may be explained by weaker purifying selection and a widespread genetic hitchhiking. Here we discuss how the unique genomic features of pericentromeric location of the papaya sex-determining region may have influenced its evolution.