More specifically, sex determination has so far proven to be a result of one of the following three mechanisms: a Environmental action on the embryo at a crucial stage of development. Temperature-dependent sex determination and gonadal differentiation in reptiles.
From Wikipedia, the free encyclopedia. Reproduction, Fertility, and Development. In birds however, females are the heterogametic sex, carrying one copy of each of the so called Z and W sex chromosomes, whereas males are homogametic ZZ. For example, in human cultures where keeping cows and consumption of fresh milk has been tradition for a long time, most adults can digest lactose.
Cytogenetics : chromosomes.
New York: Pergamon Press; Manolakou, P. Sexual selection. On the other hand, X-Y recombination is limited to the two pseudoautosomal regions, i. Help Community portal Recent changes Upload file. Current Science.
Social Research. It is surprising that the mechanism for sex determination is not as universal as the processes of meiosis and fertilization on which sexual reproduction depends. American Journal of Medical Genetics. These species' sex chromosomes are relatively primitive and unspecialized.
In reptiles, the gene is not differentially expressed in response to temperature variation during the TSP, therefore, its role in reptile sex determination is unclear. A series of intricate gene interactions that can take it from there and establish the development of the appropriate sex.
Either, as in mammals, the expression of a gene on the Y-chromosome determines male differentiation. Fish genomes, comparative genomics and vertebrate evolution. Some species use a specific permanent habitat while others occur in different habitats or change habitat with age.