Evolutionary Dynamics of Sex Chromosomes
Summary
Sex chromosome evolution arises from the differentiation of autosomes into distinct male and female chromosomes through the suppression of recombination between homologues. Initial divergence often begins with the acquisition of a sex-determining locus, followed by stepwise reduction of recombination that leads to degeneration of the heterogametic partner, as exemplified by the mammalian Y or the avian W chromosome. This process engenders asymmetries in gene dosage, which are countered by dosage compensation mechanisms that equalise expression across sexes. Hemizygosity of sex chromosomes exposes recessive mutations to selection, fostering accelerated rates of adaptive change—a phenomenon known as faster-X or fast-Z evolution—while reduced effective population size can magnify genetic drift. Neo-sex chromosomes, formed by recent fusion events between autosomes and existing sex chromosomes, provide natural experiments for studying early stages of degeneration, dosage effects and reproductive isolation. Patterns of introgression and hybridisation at sex-linked loci often reveal barriers to gene flow, underlining the role of sex chromosomes in speciation. Comparative studies across taxa—from fish and insects to birds and mammals—have elucidated how mating systems, life-history traits and demographic history modulate the tempo of sex chromosome evolution. Beyond fundamental insights, this research has practical implications for biodiversity conservation, pest management and understanding human genetic disorders linked to sex chromosome abnormalities.
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Evolutionary Dynamics of Sex Chromosomes publication trend
The graph below shows the total number of articles in evolutionary dynamics of sex chromosomes across all publications each year (not limited to Nature Index journals).
Technical terms
Hemizygosity: The condition of possessing only one copy of a chromosome or gene locus, as seen in the heterogametic sex.
Dosage compensation: The process by which organisms equalise expression of sex-linked genes between sexes despite differences in chromosome copy number.
Faster-X/Fast-Z evolution: Accelerated rate of sequence divergence on sex chromosomes compared with autosomes, driven by selection on recessive alleles or reduced effective population size.
Neo-sex chromosomes: Newly formed sex chromosomes resulting from fusion events between autosomes and ancestral sex chromosomes.
Introgression: The incorporation of genetic material from one species or population into another via hybridisation and backcrossing.
References
- Recent secondary contact, genome-wide admixture, and asymmetric introgression of neo-sex chromosomes between two Pacific island bird species. PLOS Genetics (2024).
- Sex chromosome heteromorphism and the Fast‐X effect in poeciliids. Molecular Ecology (2023).
- Role-reversed polyandry is associated with faster fast-Z in shorebirds. Proceedings of the Royal Society B (2024).
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