chapter 21

Question 1

natural selection

Answer 1

the process in which, when there is inherited variation in a population of organisms, the variants best suited for growth and reproduction in a given environment contribute disproportionately to future generations

Question 2

gene pool

Answer 2

all the alleles present in all individuals in a population or species

Question 3

population

Answer 3

all the individuals of a given species that live and reproduce in a particular place

Question 4

deleterious mutation

Answer 4

harmful effect on an organism

Question 5

neutral mutation

Answer 5

little or no effect on an organism

Question 6

advantageous mutation

Answer 6

improve their carriers’ chances of survival or reproduction

Question 7

adaptation (adapted)

Answer 7

in an evolutionary context, the fit between an organism and its environment the results from evolution by natural selection

Question 8

allele frequency

Answer 8

among all the alleles of a gene in a population, the proportion that are a specified allele

Question 9

fixation (fixed)

Answer 9

population exhibits only one allele at a particular gene

Question 10

Hardy-Weinberg equilibrium

Answer 10

describes the situation in which evolution does not occur

Question 11

genetic drift

Answer 11

a change in the frequency of an allele due to the random effects of limited population size

Question 12

non-random mating

Answer 12

when individuals do not mate randomly

Question 13

Modern Synthesis

Answer 13

the current theory of evolution, which combines Darwin’s theory of natural selection and Mendelian genetics

Question 14

positive selection

Answer 14

natural selection that increases the frequency of a favorable allele

Question 15

negative selection

Answer 15

natural selection that decreases the frequency of a deleterious allele

Question 16

balancing selection

Answer 16

natural selection that acts to maintain two or more alleles of a given gene in a population

Question 17

heterozygote advantage

Answer 17

a form of balancing selection in which the heterozygote’s fitness is higher than that of either of the homozygotes, resulting in selection that ensures that both alleles remain in the population at intermediate frequencies

Question 18

stabilizing selection

Answer 18

maintains the status quo and acts against extremes

Question 19

directional selection

Answer 19

leads to a change in a trait over time

Question 20

disruptive selection

Answer 20

operates in favor of extremes and against intermediate forms

Question 21

artificial selection

Answer 21

a form of directional selection analogous to natural selection, but without the competitive element

Question 22

migration

Answer 22

the movement of individuals from one population to another

Question 23

sexual selection

Answer 23

promotes traits that increase an individual’s access to reproductive opportunities

Question 24

intersexual selection

Answer 24

focuses on the interactions between females and males

Question 25

intrasexual selection

Answer 25

focuses on interactions between individuals of one sex

Question 26

gene flow

Answer 26

the movement of alleles from one population to another

Question 27

bottleneck

Answer 27

occurs when an originally larger population falls to just a few individuals

Question 28

founder effect

Answer 28

when a few individuals start a new population

Question 29

molecular evolution

Answer 29

evolution at the level of DNA, which in time results in the genetic divergence of populations

Question 30

molecular clock

Answer 30

estimates of the time when different taxa diverged, based on the amount of genetic divergence between them