Compared to the X, the Y is essentially a runt of a chromosome: stunted and with significantly less genetic material. When it comes to chromosomes, however, it’s not size that matters, it’s what you code with it. And the Y is indeed home to a very significant sex-determining gene called SRY (standing for Sex- determining Region of the Y). In the 1980s Peter Goodfellow’s lab in London finally unmasked this unassuming piece of genetic code as the elusive testis-determining factor in humans.
