Humans have 23 pairs of chromosomes, but only one pair determines our sex: the X and Y chromosome. The Y-chromosome differentiates between male and females; males have the Y-chromosome, females do not. However, this may not have always been the case. The Y-chromosome is substantially smaller than the X-chromosome, in terms of base pairs and functional genes. The Y-chromosome has about two hundred functional genes, while the X-chromosome has over a thousand genes.
A recently study conducted by a team of scientist composed of Henrik Kaessmann, Associate Professor at the CIG (UNIL) and group leader at the SIB Swiss Institute of Bioinformatics, and their collaborators in Australia released findings that the X and Y chromosomes were once identical and around 180 million years ago the Y chromosome began to lose non-essential genes and became unique to eutherian males. They compared the three types of mammals; egg-laying mammals such as the platypus, marsupials like the opossum, and eutherians, which include humans. They sequenced DNA from non-determining chromosome in both platypuses and opossums, and sex-determining chromosomes in eutherian mammals and found the Y-chromosome splits about 180 million years back. Through evolution, elements common between the X and Y chromosomes, not related to sex, became functionless and lost in the Y chromosome. This caused the chromosome to shrink and made it the sole factor in determining sex in eutherian mammals. The scientist predict that, at its current rate of evolution, the Y-chromosome might eventual disappear completely. However, this wouldn’t be the end of males..They predict another split would have to occur in order to maintain sex determination.
The Y sex-chromosome evolved from the X non-sex-determining chromosome. The SRY gene, found on the Y chromosome, is one of the major genes responsible for the development of testes. Its expression is present in both platypuses and eutherians. This is one of the essential elements that survived the split and was a useful gene in tracing the split between chromosomes.
Maxwell Liner (B)