Evolution__3rd_Edition

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Evolutionary
Genetics
Part two
The theory of population genetics is the most important, most fundamental body of theory
in evolutionary biology. It is the proving ground for almost all ideas in evolutionary
biology. The coherence of an evolutionary hypothesis usually remains in doubt until
the hypothesis is expressed in the form of a population genetic model. We start with the
simplest, and move on to the more complex, cases. The simplest case is when the population
is large, large enough that we can ignore random effects; models of this kind are called
deterministic. In Chapter 5, we look at a simple deterministic model of natural selection. The
model has only one genetic locus, and one allele of higher fitness is being substituted for an
inferior allele. We also look at how natural selection can maintain variation at a single locus,
in three circumstances, and look at examples of each.
Chapter 6 considers random effects in population genetics. The transfer of genes from
one generation to the next is not a perfectly exact process, because random sampling may
change the frequency of a gene. The effects of random sampling are most powerful when
the different genotypes all have the same fitness, and when population sizes are small. The
theory of random drift has been most important for thinking about molecular evolution.
Chapter 7 looks at the relative contributions of random drift and natural selection to molecular
evolution. The question of their relative contributions has stimulated one of the richest
research programs in evolutionary biology. We shall concentrate on modern research, but
look at its conceptual roots too.
In Chapter 8, we move on to consider natural selection working simultaneously on more
than one locus. Linkage between loci complicates the one-locus model. With more than one
locus, the genes at different loci may interact and influence each other’s fitness. Evolution
at one locus can be influenced by genes at other loci. It is a matter of controversy how