How is sex determined?

Sex is one of the most universal and important biological phenomena, but its underlying mechanism is unexpectedly labil throughout evolution. Sex determination usually occurs during early development, when genetic or environmental cues commit the biopotential gonad to differentiate into either testis or ovary. We are collecting transcriptomes from several vetebrate species embryos, in order to identify the unknown master sex-determining genes, and seek to answer how is sex determined, and why the molecular mechanism is so diverse across speices?

What drives the sex chromosome pair to diverge?

Once the sex-determining gene originated, there will be selection for recombination suppression between the sex chromosome pair, to avoid, for example, male-determining gene being transmitted into females through recombination onto the X chromosome. Previous works in mammals and birds have found a punctuated mode of recombination loss, forming a pattern termed 'evolutionary strata'. Our lab is an active member of Avian Genomics Consortium, which aims to sequence the genomes of all the bird speices (~10,000 speices, 'B10K' project). We are currently analyzing the avaiable ~200 female bird genomes, and trying to reconstruct a fine history map of bird sex chromosome evolution.

How does the Y/W chromosome degenerate?

After Y or W chromosome has lost the homologous recombination, they would inevitably accumulate deleterious mutations and start to degenerate in function. This is demonstrated by the nearly universally repetitive and gene-poor Y or W chromosomes of extant species, including most model speices like human and Drosophila melanogaster. It is therefore difficult to study how and why Y/W chromosomes degenerate in these species. We harness the recently-born sex systems ('neo-sex') of Drosophila and birds, and intend to study the genomic and epigenomic evolution of Y or W chromosomes.