Cam xy sex
Genes homologous to the mammalian X are located on chicken chromosomes 1, 4 and 12.Nearly 40 years later the basis of Ohno’s hypothesis still stands, although it now requires some modification.(1) The marsupial X chromosome differs from the eutherian X chromosome in that genes homologous with the short arm of the human X are autosomal and do not require dosage compensation (Spencer et al., 1991).(2) The chloride channel gene (CLCN4) is X-linked and X-inactivated in humans and Mus spretus but maps to chromosome 7 in Mus musculus (Palmer et al., 1995).It is singled out in this review because of its likely key role in sex determination both in birds and in reptiles with TSD.DMRT1 is one of the few sex genes that have been mapped in representative species of fish, turtles, crocodiles, amphibians, birds and mammals.Disorders of sex determination are not lethal and so provide an excellent model for the study of biological systems.Introduction to this fascinating field was initially through the study of numerical and structural abnormalities of the human sex chromosomes, prompted by the paradoxical nuclear sex chromatin findings that were widely thought to indicate that Turner and Klinefelter syndromes were sex reversed males and females respectively.Genetic sex determination (GSD) occurs in most species, although temperature-dependent sex determination (TSD) is the switch in some reptiles without GSD.
The solution of these problems has required the collaboration and expertise of geneticists and molecular biologists.The conservation in form and gene content of X chromosomes in all mammalian species is explained by the two processes of meiotic isolation and X-inactivation.