ABSTRACT
Sex determination is a fundamental aspect of avian biology. Differentiation of the sexes during embryonic development is essential for later reproduction and survival of the species. All birds have genetic sex determination, in which sex is established at fertilisation by the inheritance of sex chromosomes. Most birds have identifiable sex chromosomes (ZZ male; ZW female). This chapter will review our current understanding of sex determination in avians, based primarily on studies in the chicken (Gallus gallus domesticus). The chicken has long been used as a model in developmental biology, and is a species of agricultural importance. At present, the molecular mechanism of sex determination in chickens and other birds is not known. However, a draft sequence of the chicken genome has now been reported, providing new genetic data, which will help to elucidate the mechanism of avian sex determination (International Chicken Genome Sequencing Consortium 2004; Schmid et ah 2005).
