<P> By 7 weeks, a fetus has a genital tubercle, urogenital groove and sinus, and labioscrotal folds . In females, without excess androgens, these become the clitoris, urethra and vagina, and labia </P> <P> Differentiation between the sexes of the sex organs occurs throughout embryological, fetal and later life . This includes both internal and external genital differentiation . In both males and females, the sex organs consist of three structures: the gonads, the internal genitalia, and the external genitalia . In males, the gonads are the testes and in females they are the ovaries . These are the organs that produce gametes (egg and sperm), the reproductive cells that will eventually meet to form the fertilized egg (zygote). </P> <P> As the zygote divides, it first becomes the embryo (which means' growing within'), typically between zero and eight weeks, then from the eighth week until birth, it is considered the fetus (which means' unborn offspring'). The internal genitalia are all the accessory glands and ducts that connect the gonads to the outside environment . The external genitalia consist of all the external reproductive structures . The sex of an early embryo cannot be determined because the reproductive structures do not differentiate until the seventh week . Prior to this, the child is considered bipotential because it cannot be identified as male or female . </P> <P> The internal genitalia consist of two accessory ducts: mesonephric ducts (male) and paramesonephric ducts (female). The mesonephric system is the precursor to the male genitalia and the paramesonephric to the female reproductive system . As development proceeds, one of the pairs of ducts develops while the other regresses . This depends on the presence or absence of the sex determining region of the Y chromosome, also known as the SRY gene . In the presence of a functional SRY gene, the bipotential gonads develop into testes . Gonads are histologically distinguishable by 6--8 weeks of gestation . </P>

Gonadal differentiation begins at approximately what point after conception
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