Introduction to Genetic Analysis 631

Introduction to Genetic Analysis 631 - Fitness is a...

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Unformatted text preview: Fitness is a consequence of the relation between the phenotype of the organism and the environment in which the organism lives, so the same genotype will have different fitnesses in different environments. One reason is that even genetically identical organisms may develop different phenotypes if exposed to different en- vironments during development. But, even if the pheno- type is the same, the success of the organism depends on the environment. Having webbed feet is fine for pad- dling in water but a positive disadvantage for walking on land, as a few moments spent observing how a duck walks will reveal. No genotype is unconditionally supe- rior in fitness to all others in all environments. Reproductive fitness is not to be confused with physical fitness in the everyday sense of the term, al- though they may be related. No matter how strong, healthy, and mentally alert the possessor of a genotype may be, that genotype has a fitness of zero if for some reason its possessors leave no offspring. The fitness of a genotype is a consequence of all the phenotypic effects of the genes involved. Thus, an allele that doubles the fe- cundity of its carriers but at the same time reduces the average lifetime of its possessors by 10 percent will be more fit than its alternatives, despite its life-shortening property. The most common example is parental care....
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