Genomic origins of insect sex chromosomes

• Insect sex chromosomes often lack homology even among closely related lineages.
• Rates of loss and gain of Y chromosomes may be related to the mechanism of male meiosis.
• Transposons may rewire gene regulation to compensate X-linked genes for loss of Y homologs.
• Heteromorphic sex chromosomes can revert to autosomal inheritance.
• To know if perspectives biased toward XY systems hold in ZW lineages will require broader sampling.

Recent efforts to catalog the diversity of sex chromosome systems coupled with genome sequencing projects are adding a new level of resolution to our understanding of insect sex chromosome origins. Y-chromosome degeneration makes sequencing difficult and may erase homology so rapidly that their origins will often remain enigmatic. X-chromosome origins are better understood, but thus far prove to be remarkably labile, often lacking homology even among close relatives. Furthermore, evidence now suggests that differentiated X or Y-chromosomes may both revert to autosomal inheritance. Data for ZW systems is scarcer, but W and Y-chromosomes seem to share many characteristics. Limited evidence suggests that Z-chromosome homology is more conserved than X counterparts, but broader sampling of both sex chromosome systems is needed.