What gene on the Y chromosome is crucial for testicular determination?

The SRY (Sex-determining Region Y) gene is essential for testicular determination because it initiates male sex differentiation. Located on the Y chromosome, the SRY gene encodes a transcription factor that triggers the development of the testes from the primordial gonads. In the presence of SRY, these structures will mature into testes, which in turn produce male hormones such as testosterone that contribute to the development of male physical characteristics.

While SOX9, which is also involved in the sex differentiation process, plays a role after the SRY gene has activated the testicular development, it is the SRY that serves as the pivotal switch for initiating the pathway toward male sex determination. The other genes listed, such as LH and HCG, are hormones important in processes related to reproductive function but do not play a direct role in the initial determination of gonadal sex.