Chapter 21

Question 1

Adaptation

Answer 1

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.

Question 2

Allele

Answer 2

The alternate form of a genetic character found at a given locus on a chromosome.

Question 3

Artificial selection

Answer 3

The selection by plant and animal breeders of individuals with certain desirable traits.

Question 4

Clinal Variation

Answer 4

Gradual change in the phenotype of a species over a geographic gradient

Question 5

Directional Selection

Answer 5

Selection in which phenotypes at one extreme of the population distribution are favored. (Contrast with disruptive selection, stabilizing selection.)

Question 6

Disruptive Selection

Answer 6

Selection in which phenotypes at both extremes of the population distribution are favored. (Contrast with directional selection; stabilizing selection.)

Question 7

Fitness

Answer 7

The contribution of a genotype or phenotype to the genetic composition of subsequent generations, relative to the contribution of other genotypes or phenotypes

Question 8

Founder effect

Answer 8

Random changes in allele frequencies resulting from establishment of a population by a very small number of individuals.

Question 9

Frequency-dependent selection

Answer 9

Selection that changes in intensity with the proportion of individuals in a population having the trait.

Question 10

Gene Flow

Answer 10

Exchange of genes between populations through migration of individuals or movements of gametes.

Question 11

Gene pool

Answer 11

All of the different alleles of all of the genes existing in all individuals of a population.

Question 12

Genetic drift

Answer 12

Changes in gene frequencies from generation to generation as a result of random (chance) processes.

Question 13

Genetic Structure

Answer 13

The frequencies of different alleles at each locus and the frequencies of different genotypes in a Mendelian population.

Question 14

Hardy-Weinberg Equilibrium

Answer 14

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.

Question 15

Heritable Trait

Answer 15

A trait that is at least partly determined by genes.

Question 16

Mutation

Answer 16

A change in the genetic material not caused by recombination.

Question 17

Natural Selection

Answer 17

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.

Question 18

Neutral Allele

Answer 18

An allele that does not alter the functioning of the proteins for which it codes.

Question 19

Population

Answer 19

Any group of organisms coexisting at the same time and in the same place and capable of interbreeding with one another.

Question 20

Population Bottleneck

Answer 20

A period during which only a few individuals of a normally large population survive.

Question 21

Sexual Selection

Answer 21

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.

Question 22

Stabilizing Selection

Answer 22

Selection against the extreme phenotypes in a population, so that the intermediate types are favored. (Contrast with disruptive selection.)

Question 23

Trade-off

Answer 23

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.