B The potential for sexually antagonistic polymorphism in different genome regions. However, for the complete elimination of the Y to occur, an alternative way of sex determination must have evolved such as by determining sex from the ratio of X chromosomes to autosomesand any genes required for male function must have been translocated to other chromosomes.
In humans and many other species of animals, the father determines the sex of the child. Here we survey our current understanding of how and why sex determination evolves in animals and plants and identify important gaps in our knowledge that present exciting research opportunities to characterize the evolutionary forces and molecular pathways underlying the evolution of sex determination.
Mol Phylogenet Evol — One hypothesis is that occasional X-Y recombination purges deleterious alleles on the Y. Takehana, Y. Sex determination: the mechanism by which the sexual phenotype of an individual is established in a given species.
Also interesting is that gene model of sex chromosome evolution of humans in Davenport has played an important role in Drosophila Y chromosome evolution 27and the Drosophila Y chromosome influences expression of possibly hundreds of autosomal and X-linked genes 31 - The first is Charlesworth and Charlesworth's [ 10 ] exploration of the evolution of sex chromosomes and separate sexes from an initially hermaphroditic state, and the second is Rice's [ 65 ] model of sexual antagonism favouring recombination suppression in systems with established sexes e.
Conservation of Y-linked genes during human evolution revealed by comparative sequencing in chimpanzee. Wang, P. Male D. Heterochromatin A tightly packed form of DNA, that is typically genetically inactive, and contains repetitive sequences and few genes. Genetic analysis of the male fertility factors on the Y-chromosome of Drosophila melanogaster.
Despite the elaborate structure of the chimpanzee Y, there are no chimpanzee-specific ampliconic genes, yet three out of nine multi-copy, testis-expressed gene families present in human are pseudogenized or are simply absent in chimpanzee. The picture that emerges from the Silene data is one of a progressive suppression of recombination, gradually diminishing the PAR.
Molecular characterization of young sex chromosomes in several plant species is ongoing 79 , and recently, the first Y-linked genomic sequence was published from papaya The recombination suppression region of the proto-sex chromosomes can expand further via the accumulation of sexually antagonistic genes i.
In any case, the field of sex chromosome evolution seems likely to remain active and dynamic for many years to come.