Non-AIS males have a relatively large X and a small Y sex chromosome and normal females have two X sex chromosomes. When the germ, or generative cells, are formed in the body of the adult, these sex chromosomes become separated, so that a sperm carries either a single X or a single Y chromosome, whilst every egg carries a single X chromosome. Thus the sperm controls the genetic sex of the child. Although the sex of the embryo is determined at the time of conception, anatomical differences don't show until approximately two months later. Gonad is the term given to the undifferentiated organ that will later become either a testis an ovary.
Testes develop earlier than ovaries.
In an XY foetus, the gonads develop into testes. The testes then cause the Wolffian ducts to develop into the rest of the internal male system, and the Mullerian ducts to be suppressed. In an XX foetus, the gonads develop into ovaries, the Mullerian ducts then form the rest of the female internal system and the Wolffian ducts are suppressed. It is important to understand not only that there is a single primitive structure in the indifferent stage from which the male or the female organs develop, but that, each reproductive organ in either sex has a counterpart in the opposite sex. For example, the penis of the male and the much smaller clitoris of the female both come from the embryonic genital tubercle or phallus.