Evolution of Asymmetry in Sexual Reproduction
Sexual reproduction is a widespread phenomenon. In most higher organisms it is the only mode of reproduction, while many lower organisms have the capacity to reproduce both asexually and sexually. There are few species in which sexual reproduction never has been observed. Sex can be characterized by the following three processes: fusion of two haploid sex cells (called gametes) into a (diploid) zygote, recombination of the genetic information from both gametes, and production of a new generation of haploid gametes. Although the processes involved are known into considerable detail, there is still no satisfactory functional explanation for the evolution of sex. In short, the problem is that it is difficult to explain the origin and maintenance of sex in terms of any benefit to individual fitness (fitness is a measure of the probability of survival and reproduction). The conclusion from theoretical analysis is that there should be strong selection pressure favouring the abandonment of sex by females, and the adoption of asexual reproduction instead. An extensive discussion of this matter can be found in Maynard Smith (1978).
KeywordsDepression Recombination Librium Chlamydomonas Tunicamycin
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