An Evolutionary Advantage of Haploidy in Large Yeast Populations

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Science  24 Jan 2003:
Vol. 299, Issue 5606, pp. 555-558
DOI: 10.1126/science.1078417

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Although seed plants and multicellular animals are predominantly diploid, the prominence of diploidy varies greatly among eukaryote life cycles, and no general evolutionary advantage of diploidy has been demonstrated. By doubling the copy number of each gene, diploidy may increase the rate at which adaptive mutations are produced. However, models suggest that this does not necessarily accelerate adaptation by diploid populations. We tested model predictions regarding rates of adaptation using asexual yeast populations. Adaptive mutations were on average partially recessive. As predicted, diploidy slowed adaptation by large populations but not by small populations.

  • * To whom correspondence should be addressed. E-mail: zeylcw{at}

  • Present address: Population Biology, Ecology and Evolution Program, Emory University, Yerkes Primate Research Center, 954 Gatewood Drive, Atlanta, GA 30329, USA.

  • Present address: Immunology and Infectious Diseases, Harvard School of Public Health, 665 Huntington Avenue, Boston, MA 02115–6018, USA.

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