Nature 351, 315 - 317 (23 May 1991); doi:10.1038/351315a0

Transition from haploidy to diploidy

Véronique Perrot^*†‡, Sophie Richerd^* & Myriam Valéro^*

^* Laboratoire de Génétique et Evolution des Populations Végétales, URA CNRS 1185, Bât. SN2, USTLFA, F-59 655 Villeneuve d'Ascq cedex, France
^† Zoologisches Institut der Universität, Rheinsprung 9, CH-4051 Basel, Switzerland
^‡ Present address: Zoologisches Institut der Universität, Rheinsprung 9, CH-4051 Basel, Switzerland.

As a direct consequence of sex, organisms undergo a haploid and a diploid stage during their life cycle. Although the relative duration of haploid and diploid phases varies greatly among taxa, the diploid phase is more conspicuous in all higher organisms. Therefore it is widely believed that diploidy offers more evoutionary possibilities^1–3 and is thus nearly always selected for. We have now performed computer simulations to investigate one possible advantage of diploidy, that is, protection against the expression of deleterious mutations. Instead of comparing isolated haploid and diploid populations, we considered interbreeding haploids and diploids. Diploids invaded the population only when the dominance degree of a single deleterious mutation was smaller than about 1/2, and the condition allowing diploidy to invade depended on how harmful the mutation was.

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