Regardless of why sex chromosomes originate, the process of sex chromosome evolution necessitates halting recombination between the nascent X and Y in males, or Z and W in females. Alternatively, experimental evolution of sexual conflict may prove useful in studying changes in sex-specific recombination rates.
Evolution 7— The theory of sex chromosome evolution articulated above assumes that the separation of the sexes, called gonochorism in animals and dioecy in plants, predates the evolution of sex chromosomes.
In contrast, females gain no benefit from displaying bright colours to offset increased predation, as males are not attracted to ornamented females. However, birds have only incomplete sex chromosome dosage compensation 87raising questions about the generality of the lessons from the Drosophila neo-sex chromosomes and the eutherian X-added region, as well as suggesting that the dichotomy between Drosophila and eutherians versus birds might not be heterogamety XY versus ZWbut rather complete versus incomplete dosage compensation.
Received Jan 11; Accepted May Sign up for Nature Briefing. Human genome Human Genome Project List of human genes. Help Community portal Recent changes Upload file. In most male placental mammals, homology between the X and Y sex chromosomes is limited to the small pseudo-autosomal region s PAR.
Heterochromatin, HP1 and methylation at lysine 9 of histone H3 in animals. Hermaphrodite Intersex Disorders of sex development Sex reversal.
Age First, some homomorphic sex chromosomes are young and may be in the early stages of degeneration, for example in papaya 49 Chiasmatic and achiasmatic meiosis in African eumastacid grasshoppers. For species where both sexes recombine, local sex-specific recombination rates may be important initially in sex chromosome divergence, although the mechanism for sex-specific heterochiasmy is not yet known Box 3.
Why does dosage compensation differ between XY and ZW taxa? Cartoon illustration of sex chromosome dosage compensation. Sex-specific adaptation drives early sex chromosome evolution in Drosophila.
How to make a sex chromosome. Sex-differences in recombination. Figure 2. The theory of sex chromosome evolution articulated above assumes that the separation of the sexes, called gonochorism in animals and dioecy in plants, predates the evolution of sex chromosomes. These regions, identical in both sexes, aid chromosome pairing during meiosis and ensure proper segregation.
Much of our understanding of Y chromosome decay comes from the neo-sex chromosomes in Drosophila and the X-added region of the eutherians.