EFFECTS OF SELFING ON SELECTION FOR RECOMBINATION

[摘要] This paper describes the results of computer simulations of selection on a locus which affects the rate of recombination between a pair of loci under selection. Four different models of selection for increased recombination were examined. In our first two models, which involve hitchhiking effects, increased levels of selfing can lead to increased selection for recombination, but need not always do so. With two models of selection for recombination caused by fluctuations in the environment, increased selfing always led to increased selection for recombination. Constant-environment models with nonadditive fitnesses at the two selected loci were also studied. Selfing increased selection for modifiers decreasing recombination, compared with random-mating populations in which indeed there might be no selection for decreased recombination. At high levels of selfing, the intensity of selection against recombination was sometimes found to weaken again. Six mutants of Paramecium tetraurelia with curious "Paranoiac" phenotypes have been isolated and examined. Instead of the normal transient avoiding reactions in Na+ solutions, these mutants show "violent avoidances"—backing continuously for 10 to over 60 sec. This behavior corresponds to prolonged membrane excitation.—Genetic analyses establish five genic loci at which mutations give the "Paranoiac" phenotype. Close linkage between two of these genes occurs. Allelic variants are found for two of the genes. In one case, the two alleles determine very different behavioral phenotypes ("Paranoiac" and "fast-2"). These results show that the mechanism(s) which shuts off excitation in the wild-type membrane is (are) complex, but in the future may be fruitfully pursued in mutants which are defective.

[学科分类] 医学（综合）