The role of Sexual Reproduction in the Elimination of Deleterious mutations

摘要

From the 1970s onwards evolutionary biologists have been reconsidering the evolution of sexual reproduction. In view of the fact that in many organisms (plants, fungi, some animals) both reproductive modes are possible, maintenance of the sexual cycleby natural selection requires a short-term selective advantage to sex. This advantage should compensate for the so-called cost of sex (Maynard Smith, 1971). The cost of sex arises from the fact that an asexual female transmits every allele to all of heroffspring, while a sexual female transmits every allele on average only to half of her offspring. Therefore the genetic contribution of a parthenogenetic mutant in a sexual population is twice that of-the resident females, and the mutant is expected tospread through the population. Many potential selective advantages and disadvantages of sex as compared to asexual reproduction have been proposed (reviews are Bell (1982), Stearns (1987), and Michod and Levin (1988). At present, two hypotheses for the selective maintenance of sex predominate (Hurst and Peck,1996): the Parasite Hypothesis (Hamilton et al., 1990), emphasising the selection pressure for genetic recombination created by the presumed abundance of parasites, and the Deterministic Mutation Hypothesis (Kondrashov, 1982), which emphasises the necessity of sex to eliminate recurring deleterious mutations.