Selection coefficient 4057413 219685949 2008-06-16T12:18:35Z JackAidley 2507633 Category: biological evolution In [[population genetics]], the '''selection coefficient''' is a measure of the relative [[Fitness (biology)|fitness]] of a [[phenotype]]. Usually denoted by the letter ''s'', it compares the fitness of a phenotype to another favoured phenotype, and is the proportional amount that the considered phenotype is ''less'' fit as measured by fertile progeny. ''s''=0 then is selectively neutral compared to the favoured phenotype, while ''s''=1 indicates complete lethality. For example, if the favoured phenotype produces 100 fertile progeny, and only 90 are produced by the phenotype selected against then ''s'' = 0.1. An alternative way of expressing this is to describe the fitness of the favoured phenotype as 1.0 and that of the phenotype selected against as 0.9.<ref>Carroll, Robert L: "Patterns and Processes of Vertebrate Evolution", p.182. Cambridge University Press 1997</ref> The terminology is used in the same way to refer to the selective differences between [[genotypes]]<ref name="ridley">Ridley, Mark. [http://www.blackwellpublishing.com/ridley/a-z/Selection_coefficient.asp "Evolution - A-Z - Selection coefficient"]. Accessed [[May 23]], [[2008]]</ref> to which it extends in a natural fashion. It should be realised, however, that selection can only ever act directly on [[phenotype|phenotypic]] differences. A slightly different convention is used in the study of [[genetic drift]], where it is convenient to express selective differences both for and against a [[phenotype]] by using positive values to refer to a relative selective advantage, and negative values to refer to a relative selective disadvantage.<ref name="ridley"/> ==See also== *[[Evolutionary pressure]] [[it:Coefficiente di selezione]] {{category: biological evolution}}