Chapter 21 Flashcards
Adaptation
In evolutionary biology, a particular structure, physiological process, or behavior that makes an organism better able to survive and reproduce. Also, the evolutionary process that leads to the development or persistence of such a trait. (2) In sensory neurophysiology, a sensory cell’s loss of sensitivity as a result of repeated stimulation.
Allele
The alternate form of a genetic character found at a given locus on a chromosome.
Artificial selection
The selection by plant and animal breeders of individuals with certain desirable traits.
Clinal Variation
Gradual change in the phenotype of a species over a geographic gradient
Directional Selection
Selection in which phenotypes at one extreme of the population distribution are favored. (Contrast with disruptive selection, stabilizing selection.)
Disruptive Selection
Selection in which phenotypes at both extremes of the population distribution are favored. (Contrast with directional selection; stabilizing selection.)
Fitness
The contribution of a genotype or phenotype to the genetic composition of subsequent generations, relative to the contribution of other genotypes or phenotypes
Founder effect
Random changes in allele frequencies resulting from establishment of a population by a very small number of individuals.
Frequency-dependent selection
Selection that changes in intensity with the proportion of individuals in a population having the trait.
Gene Flow
Exchange of genes between populations through migration of individuals or movements of gametes.
Gene pool
All of the different alleles of all of the genes existing in all individuals of a population.
Genetic drift
Changes in gene frequencies from generation to generation as a result of random (chance) processes.
Genetic Structure
The frequencies of different alleles at each locus and the frequencies of different genotypes in a Mendelian population.
Hardy-Weinberg Equilibrium
In a sexually reproducing population, the allele frequency at a given locus that is not being acted on by agents of evolution; the conditions that would result in no evolution in a population.
Heritable Trait
A trait that is at least partly determined by genes.
Mutation
A change in the genetic material not caused by recombination.
Natural Selection
The differential contribution of offspring to the next generation by various genetic types belonging to the same population. The mechanism of evolution proposed by Charles Darwin.
Neutral Allele
An allele that does not alter the functioning of the proteins for which it codes.
Population
Any group of organisms coexisting at the same time and in the same place and capable of interbreeding with one another.
Population Bottleneck
A period during which only a few individuals of a normally large population survive.
Sexual Selection
Selection by one sex of characteristics in individuals of the opposite sex. Also, the favoring of characteristics in one sex as a result of competition among individuals of that sex for mates.
Stabilizing Selection
Selection against the extreme phenotypes in a population, so that the intermediate types are favored. (Contrast with disruptive selection.)
Trade-off
The relationship between the fitness benefits conferred by an adaptation and the fitness costs it imposes. For an adaptation to be favored by natural selection, the benefits must exceed the costs.
