Chapter 23

Question 1

evolutionary change below the species level; change in the allele frequency in a population over generations.

Answer 1

microevolution

Question 2

the percent, on average, of a population’s loci that are heterozygous in members of the population.

Answer 2

average heterozygosity

Question 3

a change in the nucleotide sequence of an organism’s DNA, ultimately creating genetic diversity. They also occur in the DNA or RNA of a virus.

Answer 3

mutation

Question 4

differences between the gene pools of geographically separate populations or populations subgroups.

Answer 4

geographic variation

Question 5

a graded change in a character along a geographic axis.

Answer 5

cline

Question 6

a localized group of individuals of the same species that can interbreed, producing fertile offspring.

Answer 6

population

Question 7

the aggregate of all of the alleles for all of the loci in all individuals in a population. The term is also used in a a more restricted sense as the aggregate of alleles for just one or a few loci in a population.

Answer 7

gene pool

Question 8

the condition describing a non evolving population (one that is in genetic equilibrium).

Answer 8

Hardy-Weinberg equilibrium

Question 9

the principle that frequencies of alleles and genotypes in a population remain constant from generation to generation, provided that only Mendelian segregation and recombination of alleles are at work.

Answer 9

Hardy-Weinberg principle

Question 10

a process in which change events cause unpredictable fluctuations in allele frequencies from one generation to the next. Effects are most pronounced in small populations.

Answer 10

genetic drift

Question 11

genetic drift that occurs when the size of a population is reduced, as by a natural disaster or human actions. Typically, the surviving population is no longer genetically representative of the original population.

Answer 11

bottleneck effect

Question 12

genetic drift that occurs when a few individuals become isolated from a larger population and form a new population whose gene pool composition is not reflective of that of the original population.

Answer 12

founder effect

Question 13

the transfer of alleles from one population to another, resulting from the movement of fertile individuals or their gametes.

Answer 13

gene flow

Question 14

the contribution an individual makes to the gene pool of the next generation, relative to the contributions of other individuals in the population.

Answer 14

relative fitness

Question 15

natural selection in which individuals at one end of the phenotypic range survive or reproduce more successfully than do other individuals.

Answer 15

directional selection

Question 16

natural selection in which individuals on both extremes of a phenotypic range survive or reproduce more successfully than do individuals with intermediate phenotypes.

Answer 16

disruptive selection

Question 17

natural selection in which intermediate phenotypes survive or reproduce more successfully than do extreme phenotypes.

Answer 17

stabilizing selection

Question 18

a form of natural selection in which individuals with certain inherited characteristics are more likely than other individuals to obtain mates.

Answer 18

sexual selection

Question 19

marked differences between the secondary sex characteristics of males and females.

Answer 19

sexual dimorphism

Question 20

a direct competition among individuals of one sex (usually the males in vertebrates) for mates of the opposite sex.

Answer 20

intrasexual selection

Question 21

selection whereby individuals of one sex (usually females) are choosy in selecting their mates from individuals of the other sex; also called mate choice.

Answer 21

intersexual selection

Question 22

natural selection that maintains two or more phenotypic forms in a population.

Answer 22

balancing selection

Question 23

greater reproductive success of heterozygous individuals compared with homozygotes; tends to preserve variation in a gene pool.

Answer 23

heterozygote advantage

Question 24

a decline in the reproductive success of individuals that have a phenotype that has become too common in a population.

Answer 24

frequency-dependent selection

Question 25

genetic variation that does not appear to provide a selective advantage or disadvantage.

Answer 25

neutral variation