Selection

Mechanisms of evolutionary change selection [[mutation]] [[migration models|gene flow]] [[genetic drift]] [[mutation|non-random mating]] Null model: Hardy-Weinberg Equilibrium (HWE) describes a population where no evolution is occurring. assumes: no selection, [[mutation]], [[migration models|gene flow]], [[genetic drift|drift]], mating must be random $$ p^2 + 2pq + q^2 = 1.0 $$ Measuring selection directional - favors one extreme phenotype, changes avg value of mean trait stabilizing - favors intermediate phenotypes, mean stays same disruptive - favors both extremes, leads to divergence Predict how much a trait will change in next generation: $$ R = S * h^2 $$ S= change in mean of trait within a generation after selection (survivors mean - initial mean) R= change in mean of trait from one generation to next (offspring mean - original parent mean) h^2 = realized heritability R/S

Selection at molecular level Ds = synonymous substitution rate, mutations do not change the amino acid; considered neutral Dn = non-synonymous substitution rate, mutations that do change amino acid w = Dn/Ds = type of selection. w=1 neutral, w<1 purifying, w>1 diversifying see also: [[mutations II, DNA damage and repair]] for molecular mutation mechanisms

When no single allele has a distinct advantage heterozygous advantage variable environments- different alleles favored at different times or places frequency-dependent selection- alleles are favored only when they are rare [[sexual selection]] — a distinct mode where fitness is determined by mating success