Directional selection occurs when individuals at one extreme of a trait range have higher fitness than individuals with intermediate or opposite-extreme traits. Over generations, this can shift the population toward the favored extreme.
Fitness means an individual's relative contribution of surviving offspring to later generations. If one extreme of a heritable trait improves survival or reproduction in a particular environment, individuals with that trait tend to leave more offspring. The alleles associated with the trait can then become more common.
All flashcards
Directional selection
Natural selection that favors one extreme phenotype over intermediate or opposite-extreme phenotypes, shifting the trait distribution toward the favored extreme.
Fitness
An individual's relative contribution of surviving offspring to later generations.
Hard and soft selective sweeps
A hard sweep begins with a newly arisen beneficial mutation; a soft sweep can involve beneficial variation already present in the population.
Genetic hitchhiking
The increase in frequency of nearby linked alleles as a favored genetic variant rises in frequency.
Selection limit
A slowing or cessation of phenotypic change even while directional selection continues to act.
Quiz questions
What initiates a hard selective sweep?Answer: A newly arisen beneficial mutation increases in frequency.
What can a Ka/Ks ratio greater than 1 indicate?Answer: A pattern consistent with positive selection on amino-acid-changing substitutions.
What does the QTL sign test compare when examining phenotypic divergence?Answer: The observed number of antagonistic QTL effects with a neutral expectation.
What information does a relative rate test require for evolutionary comparisons?Answer: A phylogenetic tree representing the evolutionary relationships being compared.
In a cross of two African cichlid species with different feeding styles, which structure showed evidence of directional selection in the QTL sign test?Answer: The oral jaw apparatus.