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Fetal development in mammals occurs in a highly hormonal environment with relatively high concentrations of oestrogens and progesterone and therefore during the early stages of embryonic development the testes must produce testosterone and other developmental signalling molecules in order for the testes to develop. If no testosterone is produced, the reproductive organs will take on female characteristics as a default. Abnormalities can occur if the gonads in a genetic male do not produce sufficient levels of testosterone.

Fetal development in mammals occurs in a highly hormonal environment with relatively high concentrations of oestrogens and progesterone and therefore during the early stages of embryonic development the gonads must produce testosterone and other developmental signalling molecules in order for the testes to develop. If no testosterone is produced, the reproductive organs will take on female characteristics as a default. Abnormalities can occur if the gonads in a genetic male do not produce sufficient levels of testosterone.

 

==Sex Determination in Birds==

==Sex Determination in Birds==

Birds have sex chromosomes labelled Z and W. The chromosomal requirements for a male in birds is the opposite of that in mammals as the female is the heterogametic species rather than the male. Therefore ZZ results in a male and ZW results in a female.

Birds have sex chromosomes labelled Z and W. The chromosomal requirements for a male in birds is the opposite of that in mammals as the female is the heterogametic species rather than the male. Therefore ZZ results in a male and ZW results in a female.