Chapter 21

Question 0

quantitative variation

Answer 0

Variation that is measured on a continuum (such as height in human beings) rathe than in discrete units or categories

Question 1

phenotypic variation

Answer 1

Differences in appearance or function between individual organsims

Question 2

qualitative variation

Answer 2

Variation that exists in 2 or more discrete states with intermediate forms often being absent

Question 3

polymorphism

Answer 3

The existence of discrete variants of a character among individuals in a population
“many” “form”

Question 4

If a population of skunks includes some individuals with stripes and others with spots would you describe the variation as quantitative or qualitative?

Answer 4

The variation in skunks is qualitative

Question 5

In the experiment on house mice, how did researchers demonstrate that variations in activity level had a genetic basis?

Answer 5

The researchers used artificial selection to change the activity levels of the mice

Question 6

What factors contribute to phenotypic variation in a population?

Answer 6

Genetic variation, differing environmental effects on individuals, and interactions between genes and the environment affect phenotypic variation in a populaton

Question 7

gene pool

Answer 7

The sum of all alleles at all gene loci in all individuals in a population

Question 8

genotype frequencies

Answer 8

The percentage of individuals in a population possessing a particular genotype

Question 9

allele frequencies

Answer 9

The abundance of one allele relative to others at he same gene locus in individuals of a population

Question 10

null models

Answer 10

A conceptual model that predicts what one would see if a particular factor had no effect

Question 11

Hardy-Weinberg principle

Answer 11

An evolutionary rule of thumb that specifies the conditions under which a population of diploid organisms achieves genetic equilibrium

Question 12

genetic equilibrium

Answer 12

The point at which neither the allele frequencies nor the genotype frequencies in a population change in succeeding generations

Question 13

What is the difference between the genotype frequencies and the allele frequencies in a population?

Answer 13

Genotype frequencies specify how alleles are combined in individuals, and allele frequencies specify how common the alleles are

Question 14

Why is the Hardy-Weinberg principle considered a null model of evolution?

Answer 14

The Hardy-Weinberg principle is a null model because it identifies the conditions under which evolution will not occur

Question 15

If the conditions of the Hardy-Weinberg principle are met, when will genotype frequencies stop changing?

Answer 15

If genotype frequencies are not already in equilibrium, they will stop changing after one generation of random mating

Question 16

mutation

Answer 16

a spontaneous and heritable change in DNA; rare events

Question 17

deleterious mutations

Answer 17

alter an individual’s structure function or behavior in harmful ways

Question 18

lethal mutations

Answer 18

cause great harm to organisms carrying them

Question 19

neutral mutations

Answer 19

neither harmful nor helpful

Question 20

advantageous mutation

Answer 20

a change in DNA produces which confers some benefit on an individual that carries it

Question 21

gene flow

Answer 21

The transfer of gene from one population to another through the movement of individuals or their gametes

Question 22

genetic drift

Answer 22

Random fluctuations in allele frequencies as a result of chances events; usually reduces genetic variation in a population

Question 23

population bottleneck

Answer 23

An evolutionary event that occurs when a stressful factor reduces population size greatly and eliminates some alleles from a population

Question 24

founder effect

Answer 24

An evolutionary phenomenon in which a population that was established by just a few colonizing individuals has only a faction of the genetic diversity seen in the population from which it was derived

Question 25

natural selection

Answer 25

the process by which such traits become more common in subsequent generations; the phenotype of an individual organism, rather than any particular allele

Question 26

relative fitness

Answer 26

The number of surviving offspring that an individual produces compared with the number left by others in the population

Question 27

directional selection

Answer 27

A type of selection in which individuals near one end of the phenotypic spectrum have the highest fitness

Question 28

stabilizing selection

Answer 28

A type of natural selection in which individuals expressing intermediate phenotypes have the highest relative fitness

Question 29

disruptive selection

Answer 29

A type of natural selection in which extreme phenotypes have higher relative fitness than intermediate phenotypes

Question 30

sexual selection

Answer 30

A form of natural selection established by male competition for access to females and by the females’ choice of maters

Question 31

sexual dimorphism

Answer 31

Differences in size or appearance of males and females

Question 32

Inbreeding

Answer 32

A special form of nonrandom mating in which genetically related individuals mate with each other

Question 33

Which agents of microevolution tend to increase genetic variation within populations, and which ones tend to decrease it?

Answer 33

Mutation and gene flow tend to increase genetic variation within population and natural selection and genetic drift tend to decrease it

Question 34

Which mode of natural selection increases the representation of the average phenotype in a population?

Answer 34

Stabilizing selection increases the representation of the average phenotype in a population

Question 35

In what ways is sexual selection like directional selection?

Answer 35

Sexual selection, like directional selection, favors extreme phenotypes.

Question 36

balanced polymorphism

Answer 36

The maintenance of 2 or more phenotypes in fairly stable proportions over many generations

Question 37

heterozygote advantage

Answer 37

an evolutionary circumstance in which individuals that are heterozygous at a particular locus have higher relative fitness that either homozygote

Question 38

frequency-dependent selection

Answer 38

a form of natural selection in which rare phenotypes have a selective advantage simply because they are rare

Question 39

neutral variation hypothesis

Answer 39

An evolutionary hypothesis that some variation at gene loci codin g for enzymes and other soluble proteins is neither favored nor eliminated by natural selection

Question 40

How does the diploid condition protect harmful recessive alleles from natural selection?

Answer 40

Diploidy protects harmful recessive alleles because dominant alleles mask their effects in heterozygotes

Question 41

What is balanced polymorphism?

Answer 41

A balanced polymorphism is one in which 2 or more phenotypes are maintained in fairly stable proportions over many generations

Question 42

Why is the allele that causes sickle-cell disease very rare in human populations that are native to northern Europe?

Answer 42

The sickle-cell allele is rare in Northern Europe because in the absence of the malarial parasite, it confers no advantage on individuals that carry it.

Question 43

adaptation

Answer 43

the accumulation of adaptive traits over time; examples that range across all levels of biological organization, from the molecular to the ecological

Question 44

How can a biologist test whether a trait is adaptive?

Answer 44

The adaptive value of a trait can be evaluated by comparing closely related species that live in different environments

Question 45

Why are most organisms adapted to the environments in which their parents lived?

Answer 45

Natural selection preserves traits that were useful when the organisms subject to selection were alive and reproducing