The key factor that determines whether the undifferentiated gonads develop into testes is the A. secretion of testosterone from the adrenals. B. secretion of androgens from the gonads. C. gene Sry located on the X chromosome. D. 21st pair of chromosomes. E. gene Sry located on the Y chromosome.

E

Explanation:

During genital sex differentiation, a series of events are involved in which the sexually indifferent embryo progressively acquires the male or female characteristics in the gonads, genital tract and the external genitalia.

The key factor that determines the development of undifferentiated gonads into testes is a single gene known as the SRY, located on the Y chromosome.