DETECTION OF DELETERIOUS GENOTYPES IN MULTIGENERATIONAL STUDIES - II - THEORETICAL AND EXPERIMENTAL DYNAMICS WITH SELFING AND SELECTION

A mathematical model was developed to help interpret genotype and alle le frequency dynamics in selfing populations, with or without apomixis . Our analysis provided explicit time-dependent solutions for the freq uencies at diallelic loci in diploid populations under any combination of fertility, viability, and gametic selection through meiotic drive. With no outcrossing, allelic variation is always maintained under gam etic selection alone, but with any fertility or viability differences, variation will ordinarily be maintained if and only if the net fitnes s (fertility x viability) of heterozygotes exceeds that of both homozy gotes by a substantial margin. Under pure selfing and Mendelian segreg ation, heterozygotes must have a twofold fitness advantage; the level of overdominance necessary to preserve genetic diversity declines with apomixis, and increases with segregation distortion if this occurs eq ually and independently in male and female gametes. A case study was m ade of the Arabidopsis act2-1 actin mutant over multiple generations i nitiated from a heterozygous plant. The observed genotypic frequency d ynamics were consistent with those predicted by our model for a delete rious, incompletely recessive mutant in either fertility or viability. The theoretical framework developed here should be very useful in dis secting the form(s) and strength of selection on diploid genotypes in populations with negligible levels of outcrossing.