<P> The genetic sex is determined by whether a Y bearing or next bearing sperm fertilizes the open; the presence or absence of a Y chromosome in turn determines whether the gonads of the embryo will be testes or ovaries; and the presence or absence of testes, finally, determines whether the sex accessory organs and external genitalia will be male or female . This sequence is understandable in light of the fact that both male and female embryos develop within the maternal environment - high in estrogen secreted by the mother's ovaries and the placenta . If estrogen determined the gender, all embryos would become feminized . </P> <P> During puberty increased gonadotropin secretion stimulates a rise in sex steroids creation from the testes . The increased secretion of testosterone from the testes during puberty causes the male secondary sexual characteristics to be manifested . </P> <P> the manifestation of secondary sexual characteristics include the growth of: </P> <Ul> <Li> testes </Li> <Li> pubic hair </Li> <Li> the whole body </Li> <Li> penis </Li> <Li> larynx </Li> <Li> facial and axillary hair </Li> </Ul>

What are the three main functions of the male reproductive system