SEX DETERMINATION AND CONTROL MECHANISMS IN BIRDS

The modern conception of genetic bases of bird's sex determination is considered. Following the genotypic mechanism of sex determination, birds implement a complex system of sex chromosome relationships. Z chromosome contains a dose-dependent male sex determinant ? gene DMTR1 ensuring the testicles development upon two copy availability in the ZZ combination. Some factors on the W hromosome are not yet identified. On the one hand, they suppress the activity of the DMTR1 gene and on the other hand they activate aromatase enzyme, which in ZW combination promotes the female sex development. It was suggested that while a number of different classes of animal adaptations are appeared ensuring stable embryo development, the dependence of sex determination upon environment and inner signals at the later stages of embryogenesis is reduced. At the same time, sex determinants fixed on genetic level are appeared that are active at the very early stages of development.