AP Bio Midterm Key Terms Ch. 23

Question 1

average heterozygosity

Answer 1

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

Question 2

balanced polymorphism

Answer 2

The ability of natural selection to maintain diversity in a population.

Question 3

balancing selection

Answer 3

Natural selection that maintains stable frequencies of two or more phenotypic forms in a population (balanced polymorphism).

Question 4

bottleneck effect

Answer 4

Genetic drift resulting from the reduction of a population, typically by a natural disaster, such that the surviving population is no longer genetically representative of the original population.

Question 5

cline

Answer 5

A graded variation in a trait that parallels a gradient in the environment.

Question 6

directional selection

Answer 6

Natural selection that favors individuals at one end of the phenotypic range.

Question 7

disruptive selection

Answer 7

Natural selection that favors individuals on both extremes of a phenotypic range over intermediate phenotypes.

Question 8

fitness

Answer 8

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

Question 9

founder effect

Answer 9

Genetic drift that occurs when a few individuals become isolated from a larger population, with the result that the new population’s gene pool is not reflective of the original population.

Question 10

frequency-dependent selection

Answer 10

A decline in the reproductive success of a morph resulting from the morph’s phenotype becoming too common in a population; a cause of balanced polymorphism in populations.

Question 11

gene flow

Answer 11

Genetic additions to or substractions from a population resulting from the movement of fertile individuals or gametes.

Question 12

gene pool

Answer 12

The total aggregate of genes in a population at any one time.

Question 13

genetic drift

Answer 13

Unpredictable fluctuations in allele frequencies from one generation to the next because of a population’s finite size.

Question 14

genetic polymorphism

Answer 14

The existence of two or more distinct alleles at a given locus in a population’s gene pool.

Question 15

geographic variation

Answer 15

Differences between the gene pools of separate populations or population subgroups.

Question 16

Hardy-Weinberg equilibrium

Answer 16

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

Question 17

Hardy-Weinberg theorem

Answer 17

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.

Question 18

heterozygote advantage

Answer 18

Greater reproductive success of heterozygous individuals compared to homozygotes; tends to preserve variation in gene pools.

Question 19

intersexual selection

Answer 19

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

Question 20

intrasexual selection

Answer 20

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

Question 21

microevolution

Answer 21

Evolutionary change below the species level; change in the genetic makeup of a population from generation to generation.

Question 22

modern synthesis

Answer 22

A comprehensive theory of evolution emphasizing populations as units of evolution and integrating ideas from many fields, including genetics, statistics, paleontology, taxonomy, and biogeography.

Question 23

mutation

Answer 23

A rare change in the DNA of a gene, ultimately creating genetic diversity.

Question 24

neutral variation

Answer 24

Genetic diversity that confers no apparent selective advantage.

Question 25

phenotypic polymorphism

Answer 25

The existence of two or more distinct morphs (discrete forms), each represented in a population in high enough frequencies to be readily noticeable.

Question 26

polymorphism

Answer 26

The coexistence of two or more distinct forms in the same population.

Question 27

population

Answer 27

A localized group of individuals that belong to the same biological species (that are capable of interbreeding and producing fertile offspring).

Question 28

population genetics

Answer 28

The study of how populations change genetically over time.

Question 29

pseudogene

Answer 29

A DNA segment very similar to a real gene but which does not yield a functional product; a gene that has become inactivated in a particular species because of mutation.

Question 30

relative fitness

Answer 30

The contribution of one genotype to the next generation compared to that of alternative genotypes for the same locus.

Question 31

sexual dimorphism

Answer 31

A special case of polymorphism based on the distinction between the secondary sex characteristics of males and females.

Question 32

stabilizing selection

Answer 32

Natural selection that favors intermediate variants by acting against extreme phenotypes.