How Is Sex Determined in Drosophila and Humans?

Research has been conducted in order to identify the locus on the Y chromosome that initiates testis formation. The hypothetical gene was initially termed the testes-determining factor (TDF in humans, Tdy in mice) but is now known to be the same gene as that identified as SRY in humans and Sry in mice. The presence of this gene leads to male development, while its absence means that female development occurs. The SRY protein is a transcription factor expressed in the early male gonad, but it is not known precisely how it is involved in testis formation. The gene was first identified by Lovell-Badge and Goodfellow during the mapping of a genetic syndrome called sex reversal that occurs in both humans and mice. XX individuals with this syndrome are phenotypically male and have a fragment of the Y chromosome. This fragment was cloned and a transcript identified that is expressed in the developing male gonad. Lovell-Badge and Goodfellow proved that this gene was in fact the TDY / Tdy gene by inserting a fragment of the mouse chromosome including the Sry gene into a XX mouse genome. The offspring developed testes and was male both in internal and external phenotype, as would be expected if the Sry gene initiated male development.…