BIOL214 lecture 13

sampling error

higher with a smaller sample

bottleneck

reduces genetic variation; results in a non-representative set of alleles for subsequent populations, even after the population size rebounds

probability of an allele making it through a bottleneck

depends on the frequency of the allele before the bottleneck and the severity of the bottleneck

founder effect

type of bottleneck resulting from a small number of individuals colonizing a new, isolated habitat

fitness

the survival and reproductive success of an individual with a particular phenotype

components of fitness

survival to reproductive age, mating success, fecundity

relative fitness (w) 

contribution of individuals with one genotype compared with the average contribution of all individuals in the population 

average excess fitness

difference between relative contribution of individuals with one genotype and the average fitness of the population as a whole 

average excess fitness equation

large populations

where natural selection is more effective in bringing about change

pleiotropy

mutation in a single gene affects more than one phenotypic trait

antagonistic pleiotropy

beneficial effects for one trait but detrimental effects for other traits

negative selection

alleles that lower fitness experience

positive selection

alleles that increase fitness experience 

additive alleles

homozygous condition yields twice the phenotypic effect for the gene as compared with heterozygotes

dominance

dominant allele masks presence of recessive in heterozygotes

mutation-selection balance

explains persistence of deleterious mutations in populations; equilibrium frequency reached through “tug-of-war” between negative selection on deleterious alleles and new mutations

balancing selection

type of selection that favors more than one allele in order to maintain genetic diversity in a population

negative frequency-dependent selection

common phenotypes are selected against and rare phenotypes are favored

heterozygote advantage

heterozygosity confers greater fitness than homozygotes

sickle-cell anemia

example of heterozygote advantage

inbreeding depression

results in reduced fitness; rare recessive alleles are expressed in homozygous state

genetic distance

created by genetic drift; rates of divergence are dependent on population size