SRY

From Ganfyd

By default all human embryos develop as female. A trigger – the SRY gene – is responsible for switching on a genetic programme that turns the embryo into a male.

The SRY gene is found on the p arm of the Y chromosome and encodes for the testis determining factor (TDF). TDF is a DNA binding protein that enhances other transmission factors, or is possibly a transcription factor itself. Its expression causes the development of primary sex chords. These chords form in the central part of the undifferentiated gonad, turning it into a testis. The testis then starts secreting testosterone and the Anti-müllerian hormone.

If the SRY gene on a Y chromosome is sufficiently mutated that functioning TDF is not produced, the embryo will develop into an XY female. Similarly, if an SRY gene is translocated on to an X chromosome, it is possible to have an XX male.