Selective Value

The selective value (or English fitness) is a central concept in theory of the evolution. It describes the capacity of an individual of some Génotype to be reproduced. It is a measurement of the Natural selection.

One can evaluate the selective value of an individual (also called reproductive success ) by his number of descendants to the following generation.

By definition, the fitness or selective value $\ omega$ of a genotype corresponds to the number of viable and fertile descendants which on average each individual of this genotype to the following generation produces. The selective value or fitness of a genotype depends mainly on its survival between the stage zygote (egg) and the adult stage, and on its fertility (many viable descendants able to reproduce). These two parameters determine the number of descendants produced on average by this genotypic category. A simple definition of the fitness can thus be given by the formula:

Fitness = Survival X Fécondité

Absolute Fitness

One calls fitness absolute, noted W, the value resulting from the measurement of the probability of survival and the fertility of each genotypic category and which determines their median number of descendants directly. For a gene with two alleles has and has, the values of fitness will be noted in the following way: In Genetic of the populations, the absolute fitness of a genotype is evaluated by calculating the report/ratio the manpower of the descendants of the individuals having this genotype compared to manpower of the individuals parents having this genotype:

${w_ {\ mathrm {}}} =$

Relative Fitness

The performance of the genotypes is however always defined in a relative way = fitness relative noted here

\ omega

so that the strongest value of fitness is equal to 1. The relative fitness of a category of individuals is the relationship between his fitness absolute W and the strongest absolute value of fitness (Wmax) observed in the population.

Relative Fitness:

${\ omega_ {\ mathrm {}}} =$

with 0 < $\ omega$ < 1

In the case of a gene with 2 alleles has and a:

The difference between $\ omega$ and 1 is called coefficient of selection, noted S, which is a measurement of the reduction ratio of the fitness of each genotypic category compared to best in this population.

$\ omega_ {\ mathrm {AA}} = 1 - s_ {\ mathrm {AA}}$

\ omega_ {\ mathrm {Aa}} = 1 - s_ {\ mathrm {Aa}}

\ omega_ {\ mathrm {aa}} = 1 - s_ {\ mathrm {aa}}

External bonds

To carry out simulations of evolution of frequencies Al by fixing your selective values!

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