Chapter 25 (Evolutionary Processes)

Question 1

balancing selection

Answer 1

A pattern of natural selection in which no single allele is favored in all populations of a species at all times. Instead, there is a balance among alleles in terms of fitness and frequency.

Question 2

beneficial

Answer 2

In genetics, referring to any mutation, allele, or trait that increases an individual’s fitness.

Question 3

deleterious

Answer 3

In genetics, referring to any mutation or allele that reduces an individual’s fitness.

Question 4

directional selection

Answer 4

A pattern of natural selection that favors one extreme phenotype with the result that the average phenotype of a population changes in one direction. Generally reduces overall genetic variation in a population.

Question 5

disruptive selection

Answer 5

A pattern of natural selection that favors extreme phenotypes at both ends of the range of phenotypic variation. Maintains overall genetic variation in a population.

Question 6

founder effect

Answer 6

A change in allele frequencies that often occurs when a new population is established from a small group of individuals (founder event) due to sampling error (i.e., the small group is not a representative sample of the source population).

Question 7

frequency-dependent selection

Answer 7

A pattern of selection in which certain alleles are favored only when they are rare; a form of balancing selection.

Question 8

gene flow

Answer 8

The movement of alleles between populations; occurs when individuals leave one population, join another, and breed.

Question 9

gene pool

Answer 9

All of the alleles of all of the genes in a certain population.

Question 10

genetic bottleneck

Answer 10

A reduction in allelic diversity resulting from a sudden reduction in the size of a large population (population bottleneck) due to a random event.

Question 11

genetic drift

Answer 11

Any change in allele frequencies due to random events. Causes allele frequencies to drift up and down randomly over time, and eventually can lead to the fixation or loss of alleles.

Question 12

genetic variation

Answer 12

(1) The number and relative frequency of alleles present in a particular population. (2) The proportion of phenotypic variation in a trait that is due to genetic rather than environmental influences in a certain population in a certain environment.

Question 13

Hardy-Weinberg principle

Answer 13

A principle of population genetics stating that genotype frequencies in a large population do not change from generation to generation in the absence of evolutionary processes (e.g., mutation, migration, genetic drift, random mating, and selection).

Question 14

heterozygote advantage

Answer 14

A pattern of natural selection that favors heterozygous individuals compared with homozygotes. Tends to maintain genetic variation in a population. Also called heterozygote superiority.

Question 15

inbreeding depression

Answer 15

In inbred offspring, fitness declines due to deleterious recessive alleles that are homozygous.

Question 16

inbreeding

Answer 16

Mating between closely related individuals. Increases homozygosity of a population and often leads to a decline in the average fitness (inbreeding depression).

Question 17

mutation

Answer 17

Any change in the hereditary material of an organism (DNA in most organisms, RNA in some viruses).

Question 18

purifying selection

Answer 18

Selection that lowers the frequency or even eliminates deleterious alleles.

Question 19

sampling error

Answer 19

The accidental selection of a nonrepresentative sample from some larger population, due to chance.

Question 20

sexual dimorphism

Answer 20

Any trait that differs between males and females.

Question 21

sexual selection

Answer 21

A pattern of natural selection that favors individuals with traits that increase their ability to obtain mates. Acts more strongly on males than females.

Question 22

stabilizing selection

Answer 22

A pattern of natural selection that favors phenotypes near the middle of the range of phenotypic variation. Reduces overall genetic variation in a population.

Question 23

territory

Answer 23

An area that is actively defended by an animal from others of its species.