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SelectionThe Mechanism of Evolution$
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Graham Bell

Print publication date: 2007

Print ISBN-13: 9780198569725

Published to Oxford Scholarship Online: May 2008

DOI: 10.1093/acprof:oso/9780198569725.001.0001

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Natural selection in closed asexual populations

Natural selection in closed asexual populations

(p.55) CHAPTER 3 Natural selection in closed asexual populations

Graham Bell

Oxford University Press

The mechanism of evolutionary change can be studied directly through selection experiments in laboratory microcosms. This chapter begins by describing the experimental approach to evolution, and goes on to analyse adaptation over different time scales. The first section in this chapter is about microcosmologica. Subsections here concern Dallinger's experiment; the laboratory microcosm; the inhabitants of the microcosm; the selection experiment; fitness and adaptedness; and microcosm genealogy. The second section is all about sorting (in other words selection of pre-existing variation) and includes subsection on a single episode of selection; the sorting of a single type; the mixture of discrete types; the Fundamental Theorem of Natural Selection; the sorting in finite populations; drift and selection; and fluctuating population size. The third section is on purifying selection (defined as maintaining adaptedness despite genetic deterioration) and this section discusses the following: mutation-drift balance; mutation-selection equilibrium; and Muller's Ratchet. The fourth section is about directional selection (this is restoring adaptedness despite environmental deterioration) and details the probability that a beneficial mutation will be fixed; periodic selection; Fisher's geometrical analogy; the variable-mutation model; the extreme-value mode; clonal interference; the distribution of fitness effects; genetic interference; and the genetic basis of adaptation. The fifth section is about successive substitution and includes detail on phenotypic evolution towards the optimum; adaptive walks; transitivity; and clonal interference. The sixth section, Cumulative adaptation, includes the following: the protein matrix; connectance; synthetic beneficial mutations; functional interaction in a protein structure; the evolution of RNA sequences; reversibility; cumulation; cumulative construction of novel amidases; diminishing returns; and contingency. The last section called Successive substitution at several loci explains genetic interactions; the adaptive landscape; the allele matrix; compensatory mutations; compound structures; processing chains; the effect of mutation in a simple processing chain; the pattern of adaptation; the evolution of metabolic pathways; in vitro selection; genetic changes during adaptation; and repeated adaptation.

Keywords:   experimental evolution, extreme-value theory, adaptive walk, clonal interference, periodic selection, transitivity, contingency, reversibility, adaptive landscape, complex adaptations

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