Final answer:
The SRY gene, located on the Y chromosome, is essential in male sexual differentiation by initiating testis development and testosterone secretion, leading to male phenotypes and indicating absence of androgen insensitivity syndrome.
Step-by-step explanation:
The expression of the SRY gene on the Y chromosome is crucial in human embryonic development for the differentiation of the male reproductive system. When the SRY gene is expressed, it signals undifferentiated gonadal tissue to develop into testes, the male gonads. In turn, these testes begin to secrete testosterone, which is necessary for the development of male structures such as the epididymis and vas deferens, contrary to promoting the formation of the Mullerian ducts, which are precursors to female reproductive organs. Consequently, the presence of the SRY gene means that the individual does have a Y chromosome, which is typically associated with a male genotype.
Furthermore, the presence of the SRY gene and its activity is a key determinant in the development of male primary and secondary sex characteristics, thus leading to a phenotypically male individual. Also, the SRY gene's function indicates that an individual does not have androgen insensitivity syndrome (AIS), a condition where the body cannot properly respond to the androgens including testosterone, regardless of the presence of the SRY gene.