title: The effect of neutral nonadditive gene action on the quantitative index of population divergence.
abstract: For neutral additive genes, the quantitative index of population divergence (Q(ST)) is equivalent to Wright's fixation index (F(ST)). Thus, divergent or convergent selection is usually invoked, respectively, as a cause of the observed increase (Q(ST) > F(ST)) or decrease (Q(ST) < F(ST)) of Q(ST) from its neutral expectation (Q(ST) = F(ST)). However, neutral nonadditive gene action can mimic the additive expectations under selection. We have studied theoretically the effect of consecutive population bottlenecks on the difference F(ST) - Q(ST) for two neutral biallelic epistatic loci, covering all types of marginal gene action. With simple dominance, Q(ST) < F(ST) for only low to moderate frequencies of the recessive alleles; otherwise, Q(ST) > F(ST). Additional epistasis extends the condition Q(ST) < F(ST) to a broader range of frequencies. Irrespective of the type of nonadditive action, Q(ST) < F(ST) generally implies an increase of both the within-line additive variance after bottlenecks over its ancestral value (V(A)) and the between-line variance over its additive expectation (2F(ST)V(A)). Thus, both the redistribution of the genetic variance after bottlenecks and the F(ST) - Q(ST) value are governed largely by the marginal properties of single loci. The results indicate that the use of the F(ST) - Q(ST) criterion to investigate the relative importance of drift and selection in population differentiation should be restricted to pure additive traits.
authors.affiliation: Departamento de Genética, Facultad de Ciencias Biológicas, Universidad Complutense, 28040 Madrid, Spain. clfanjul@bio.ucm.es
authors.forename: Carlos
authors.initials: C
authors.lastname: López-Fanjul
authors.forename: Almudena
authors.initials: A
authors.lastname: Fernández
authors.forename: Miguel A
authors.initials: MA
authors.lastname: Toro
mesh_terms: D000483:Alleles; D000818:Animals; D004330:Drosophila / Q000235:genetics; D004843:Epistasis, Genetic; D019143:Evolution, Molecular; D005260:Female; D005787:Gene Frequency; D005796:Genes; D005799:Genes, Dominant; D005808:Genes, Recessive; D040961:Genetic Drift; D014644:Genetic Variation; D005828:Genetics, Population; D008297:Male; D008957:Models, Genetic; D008962:Models, Theoretical; D019655:Quantitative Trait, Heritable; D012641:Selection, Genetic; D014231:Tribolium / Q000235:genetics