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these epistatic interactions is the developmental pathway. Natural selection will tend to bring together those genes that constitute a balanced system. The process by which genes are accumulated in the gene pool that collaborate harmoniously is called "integration" or "coadaptation." The result of this selection has been referred to as "internal balance.'' Each gene will favor the selection of that genetic background on which it can make its maximum contribution to fitness. The fitness of a gene thus depends on and is controlled by the totality of its genetic background.
Mayr in Animal Species and Evolution (p. 295) |
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We have already looked at genetic processes at some length in the preliminary survey, so this illustration will be brief, mostly recapitulating the main points of the earlier discussion, but within the formal framework. Typically, only a certain range of basic structures, i.e., chromosomes, is admitted to studies in genetics, so that only a species, family, or other taxonomic grouping is involved. Still, in principle, one can study all possible variations, including variations in chromosome number and type. The range of the study will be primarily determined by the set W of genetic operators admitted, since the possible variants (genotypic and phenotypic) will be those produced by sequences of genetic operators from W. Familiar examples of genetic operators are mutation, crossover, inversion, dominance modification, translocation, and deletion (see the formal definitions given in chapter 6). |
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The genetic adaptive plan develops in terms of an everchanging population of chromosomes which, interacting with the environment, provides a concurrent sequence of phenotype populations. For many purposes, it is convenient to represent a population as a probability distribution over the set of genotypes  , where the probability assigned to genotype  is the fraction of the total population consisting of that genotype (cf. Crow and Kimura 1970). Thus the population at time t can be specified by  , where  is the set of distributions over . In very general terms, each element of the population is tested against the environment and is ranked according to its fitnessits ability to survive and reproduce. It's often useful to think of the environment E in terms of environmental niches, each of which can be exploited by an appropriate set of phenotypic characteristics. Then fitness µEbecomes a function of the coadapted sets of alleles which produce these characteristics (see chapter 4). From this point of view the population  can be looked upon as a reservoir of coadapted sets, preserving the history of past advances, particularly the environmental niches encountered. |
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Most mathematical models of genetic adaptation are based on very simple reproductive plans, where each individual allele si is assigned a fitness µE(si) and |
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