Compact but complex - The marsupial Y chromosome

The mammalian Y chromosome is a gene poor element with enormous responsibility. Just how the mammalian Y chromosome acquired the function of sex determination, then surrendered most of its other functions, remains one of the most intriguing questions in genomics. The basic marsupial Y chromosome represents a degraded relic of the original mammalian Y, which did not receive the large autosomal addition that augmented the X and Y of eutherian mammals. Like the Y of other mammals, the marsupial Y contains species-specific repetitive sequences. It also bears an interesting mixture of genes; ancient male-specific genes, such as SRY and RBMY, which evolved from X-borne genes before the eutherian-marsupial divergence, and are conserved across therian mammals. The marsupial Y also bears novel genes such as ATRY, that in eutherian mammals have been lost from the Y but maintain a copy on the X. The unique properties of the marsupial Y chromosome have provided insights into the evolution of the mammalian Y, enabling us to gain a better understanding of the selection processes that shaped it.