Reduced adaptation of a non-recombining neo-Y chromosome

Nature. 2002 Mar 21;416(6878):323-6. doi: 10.1038/416323a.


Sex chromosomes are generally believed to have descended from a pair of homologous autosomes. Suppression of recombination between the ancestral sex chromosomes led to the genetic degeneration of the Y chromosome. In response, the X chromosome may become dosage-compensated. Most proposed mechanisms for the degeneration of Y chromosomes involve the rapid fixation of deleterious mutations on the Y. Alternatively, Y-chromosome degeneration might be a response to a slower rate of adaptive evolution, caused by its lack of recombination. Here we report patterns of DNA polymorphism and divergence at four genes located on the neo-sex chromosomes of Drosophila miranda. We show that a higher rate of protein sequence evolution of the neo-X-linked copy of Cyclin B relative to the neo-Y copy is driven by positive selection, which is consistent with the adaptive hypothesis for the evolution of the Y chromosome. In contrast, the neo-Y-linked copies of even-skipped and roundabout show an elevated rate of protein evolution relative to their neo-X homologues, probably reflecting the reduced effectiveness of selection against deleterious mutations in a non-recombining genome. Our results provide evidence for the importance of sexual recombination for increasing and maintaining the level of adaptation of a population.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Adaptation, Biological*
  • Animals
  • Bacterial Proteins*
  • Cyclin B / genetics
  • Drosophila / genetics*
  • Drosophila Proteins / genetics
  • Evolution, Molecular*
  • Female
  • Genes, Insect
  • Homeodomain Proteins / genetics
  • Male
  • Nerve Tissue Proteins
  • Polymorphism, Genetic
  • Receptors, Immunologic / genetics
  • Recombination, Genetic*
  • Transcription Factors / genetics
  • Y Chromosome*


  • Bacterial Proteins
  • CycB protein, Drosophila
  • Cyclin B
  • Drosophila Proteins
  • En protein, Drosophila
  • Homeodomain Proteins
  • Nerve Tissue Proteins
  • Receptors, Immunologic
  • Transcription Factors
  • eve protein, Drosophila
  • roundabout protein