Selection coefficient
Encyclopedia
In population genetics
, the selection coefficient is a measure of the relative fitness
of a phenotype
. Usually denoted by the letter s, it compares the fitness of a phenotype to another favored 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 favored phenotype, while s=1 indicates complete lethality. For example, if the favored 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 favored phenotype as 1.0 and that of the phenotype selected against as 0.9. The terminology is used in the same way to refer to the selective differences between genotypes to which it extends in a natural fashion.
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.
Population genetics
Population genetics is the study of allele frequency distribution and change under the influence of the four main evolutionary processes: natural selection, genetic drift, mutation and gene flow. It also takes into account the factors of recombination, population subdivision and population...
, the selection coefficient is a measure of the relative fitness
Fitness (biology)
Fitness is a central idea in evolutionary theory. It can be defined either with respect to a genotype or to a phenotype in a given environment...
of a phenotype
Phenotype
A phenotype is an organism's observable characteristics or traits: such as its morphology, development, biochemical or physiological properties, behavior, and products of behavior...
. Usually denoted by the letter s, it compares the fitness of a phenotype to another favored 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 favored phenotype, while s=1 indicates complete lethality. For example, if the favored 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 favored phenotype as 1.0 and that of the phenotype selected against as 0.9. The terminology is used in the same way to refer to the selective differences between genotypes to which it extends in a natural fashion.
A slightly different convention is used in the study of genetic drift
Genetic drift
Genetic drift or allelic drift is the change in the frequency of a gene variant in a population due to random sampling.The alleles in the offspring are a sample of those in the parents, and chance has a role in determining whether a given individual survives and reproduces...
, where it is convenient to express selective differences both for and against a phenotype
Phenotype
A phenotype is an organism's observable characteristics or traits: such as its morphology, development, biochemical or physiological properties, behavior, and products of behavior...
by using positive values to refer to a relative selective advantage, and negative values to refer to a relative selective disadvantage.