Bio 1114; 5 - Selection and Fitness

Natural Selection

Predictable mechanism that results in a better adapted population

Characteristics of selection

Variation, selective pressure, differential survival/reproduction, heritability of characteristic

Selection differential (S)

quantifies shift in mean phenotype of population before and after selection event (population after event (p*) - population before event(p bar)

response to selection (R)

Quantifies how much the offspring generation changed because of selection (offspring mean trait after event (O*) - offspring mean before event (O bar))

Directional selection

Individuals with traits on one side or the other of mean are favored

Disruptive selection

Individuals with extreme values are favored over the mean

Stabilizing selection

Individuals with average values are favored over extreme

Viability

probability that an individual bearing genotype will sruvive

fecundity

Number of gametes per individual

Gamete viabiltiy

alleles that impact longevity or quality of sperm/egg

Mating success

Number and quality of mates

Fertilization success

Alleles impact the probability that fertilization will occur

Fitness

The average reproductive output of all organisms bearing a given genotype: integrates differences in survival and reproduction

Relative fitness (W)

relative measure of the reproductive output among known genotypes

What is the relative fitness of the FITTEST

W always equals 1