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Evolution__3rd_Edition

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<strong>Evolution</strong>ary<br />

Genetics<br />

Part two<br />

The theory of population genetics is the most important, most fundamental body of theory<br />

in evolutionary biology. It is the proving ground for almost all ideas in evolutionary<br />

biology. The coherence of an evolutionary hypothesis usually remains in doubt until<br />

the hypothesis is expressed in the form of a population genetic model. We start with the<br />

simplest, and move on to the more complex, cases. The simplest case is when the population<br />

is large, large enough that we can ignore random effects; models of this kind are called<br />

deterministic. In Chapter 5, we look at a simple deterministic model of natural selection. The<br />

model has only one genetic locus, and one allele of higher fitness is being substituted for an<br />

inferior allele. We also look at how natural selection can maintain variation at a single locus,<br />

in three circumstances, and look at examples of each.<br />

Chapter 6 considers random effects in population genetics. The transfer of genes from<br />

one generation to the next is not a perfectly exact process, because random sampling may<br />

change the frequency of a gene. The effects of random sampling are most powerful when<br />

the different genotypes all have the same fitness, and when population sizes are small. The<br />

theory of random drift has been most important for thinking about molecular evolution.<br />

Chapter 7 looks at the relative contributions of random drift and natural selection to molecular<br />

evolution. The question of their relative contributions has stimulated one of the richest<br />

research programs in evolutionary biology. We shall concentrate on modern research, but<br />

look at its conceptual roots too.<br />

In Chapter 8, we move on to consider natural selection working simultaneously on more<br />

than one locus. Linkage between loci complicates the one-locus model. With more than one<br />

locus, the genes at different loci may interact and influence each other’s fitness. <strong>Evolution</strong><br />

at one locus can be influenced by genes at other loci. It is a matter of controversy how

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