Evolution__3rd_Edition

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Full Contents ix
5.7.3 A second estimate of the fitnesses is made from the survivorship
of the different genotypes in mark–recapture experiments 111
5.7.4 The selective factor at work is controversial, but bird predation
was probably influential 112
5.8 Pesticide resistance in insects is an example of natural selection 115
5.9 Fitnesses are important numbers in evolutionary theory and can be
estimated by three main methods 118
5.10 Natural selection operating on a favored allele at a single locus is not
meant to be a general model of evolution 120
5.11 A recurrent disadvantageous mutation will evolve to a calculable
equilibrial frequency 121
5.12 Heterozygous advantage 123
5.12.1 Selection can maintain a polymorphism when the
heterozygote is fitter than either homozygote 123
5.12.2 Sickle cell anemia is a polymorphism with heterozygous
advantage 124
5.13 The fitness of a genotype may depend on its frequency 127
5.14 Subdivided populations require special population genetic principles 129
5.14.1 A subdivided set of populations have a higher proportion of
homozygotes than an equivalent fused population: this is the
Wahlund effect 129
5.14.2 Migration acts to unify gene frequencies between populations 130
5.14.3 Convergence of gene frequencies by gene flow is illustrated
by the human population of the USA 132
5.14.4 A balance of selection and migration can maintain genetic
differences between subpopulations 132
Summary Further reading Study and review questions
6. Random Events in Population Genetics 137
6.1 The frequency of alleles can change at random through time in a
process called genetic drift 138
6.2 A small founder population may have a non-representative sample
of the ancestral population’s genes 140
6.3 One gene can be substituted for another by random drift 142
6.4 Hardy–Weinberg “equilibrium” assumes the absence of genetic drift 145
6.5 Neutral drift over time produces a march to homozygosity 145
6.6 A calculable amount of polymorphism will exist in a population
because of neutral mutation 150
6.7 Population size and effective population size 151
Summary Further reading Study and review questions
7. Natural Selection and Random Drift in
Molecular Evolution 155
7.1 Random drift and natural selection can both hypothetically explain
molecular evolution 156