Relationships between Vertebrate ZW and XY Sex Chromosome Systems

Tariq Ezaz*, Rami Stiglec, Frederic Veyrunes, Jennifer A. Marshall Graves

*Corresponding author for this work

    Research output: Contribution to journalReview articlepeer-review

    176 Citations (Scopus)


    The peculiar cytology and unique evolution of sex chromosomes raise many fundamental questions. Why and how sex chromosomes evolved has been debated over a century since H.J. Muller suggested that sex chromosome pairs evolved ultimately from a pair of autosomes. This theory was adapted to explain variations in the snake ZW chromosome pair and later the mammal XY. S. Ohno pointed out similarities between the mammal X and the bird/reptile Z chromosomes forty years ago, but his speculation that they had a common evolutionary origin, or at least evolved from similar regions of the genome, has been undermined by comparative gene mapping, and it is accepted that mammal XY and reptile ZW systems evolved independently from a common ancestor. Here we review evidence for the alternative theory, that ZW⇔XY transitions occurred during evolution, citing examples from fish and amphibians, and probably reptiles. We discuss new work from comparative genomics and cytogenetics that leads to a reconsideration of Ohno's idea and advance a new hypothesis that the mammal XY system may have arisen directly from an ancient reptile ZW system.

    Original languageEnglish
    Pages (from-to)R736-R743
    JournalCurrent Biology
    Issue number17
    Publication statusPublished - 5 Sept 2006


    Dive into the research topics of 'Relationships between Vertebrate ZW and XY Sex Chromosome Systems'. Together they form a unique fingerprint.

    Cite this