The Effects of Selection on Gene Frequencies Flashcards
What is directional selection? Give an example.
A new mutation confers superior survival, becomes more and more common, and ultimately replaces a preexisting allele. E.g. melanic form of peppered moth in industrial areas
What is balancing selection? Give an example.
A number of selective processes (e.g. heterozygote advantage, frequency-dependent selection) by which multiple alleles are actively maintained in the gene pool of a population at frequencies larger than expected from genetic drift alone. It maintains stable genetic polymorphisms.
What is the coefficient of selection?
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
What is the heterozygote advantage? What are other names for this mechanism?
If the heterozygote is more fit than either homozygote.
Also known as overdominance (due to a single locus, e.g. sickle cell anemia) for fitness or heterosis (hybrid vigor, e.g. mixed breeds in dogs) for fitness.
What is frequency-dependent selection? Give an example.
The fitness of a phenotype depends on its frequency relative to other phenotypes in a given population.
In positive frequency-dependent selection, the fitness of a phenotype increases as it becomes more common, in negative, the fitness of a phenotype decreases as it becomes more common. E.g. for positive, warning coloration in snakes.
What is a polymorphism?
The existence of two or more genotypes for a given trait in a population, the rarest of which exceeds some arbitrarily low frequency.
When changes in gene frequencies are due to selection, what three things does the rate of genetic change depend on?
The magnitude of differences among genotypes, the frequencies of the alleles, and the degree of dominance.
