In mammals the male is the heterogametic species (XY chromosomes) and females are the homogametic species (XX chromosomes) and this is the first stage in the development of the reproductive system. This stage occurs in the zygote and genes in the Y chromosome regulate the development of gonads towards the male phenotype. Therefore the Y chromosome must be present for the development of the male gender, regardless of the number of X chromosomes (see Developmental Abnormalities section below). Each Y chromosome contains a '''Sex Determining Region''' (SRY) and testes must be present for the formation of male characteristics. Sex hormones produced by the developing gonads affect the further development of the reproductive organs and the nervous system and are therefore crucial. For further information in sexual differentation please see [[Sexual_Differentiation_-_Anatomy_%26_Physiology|here]]. | In mammals the male is the heterogametic species (XY chromosomes) and females are the homogametic species (XX chromosomes) and this is the first stage in the development of the reproductive system. This stage occurs in the zygote and genes in the Y chromosome regulate the development of gonads towards the male phenotype. Therefore the Y chromosome must be present for the development of the male gender, regardless of the number of X chromosomes (see Developmental Abnormalities section below). Each Y chromosome contains a '''Sex Determining Region''' (SRY) and testes must be present for the formation of male characteristics. Sex hormones produced by the developing gonads affect the further development of the reproductive organs and the nervous system and are therefore crucial. For further information in sexual differentation please see [[Sexual_Differentiation_-_Anatomy_%26_Physiology|here]]. |