The Evolutionary Life Cycle of Sex Chromosomes: Special Issue

Sex chromosomes represent a specialized component of the genome. They play an important role in basal processes such as sex determination, but are also often involved in emergent evolutionary phenomena such as speciation. How sex chromosomes are born, mature and die is a major question in contemporary evolutionary biology. Sex chromosomes are believed to evolve from an ordinary pair of autosomes, originating when an autosome pair acquires a sex-determining function. How and why this transition takes place remains largely unknown. Sex chromosomes undergo many changes, such as recombination suppression, degeneration by accumulation of repetitive DNA and transposons, dosage compensation to balance the gene products of degenerated genes, and gene trafficking to and from other chromosomes. This often yields a pair of highly-differentiated chromosomes, one of which exhibits the extensive decay characteristic of late-stage sex chromosomes. Eventually, this decrepit chromosome may even be lost, resulting in males and females having different numbers of chromosomes. Much remains to be discovered about the processes that shape sex chromosomes, but the revolution in genomics, transcriptomics and other related technologies allows us to study the evolution of sex chromosomes in unprecedented detail. This issue will address questions about the lifecycle of sex chromosomes across different organismal groups.