CHAPTER 21

Question 1

microevolution

Answer 1

change in allele frequencies in a population over generations

Question 2

genetic variation

Answer 2

differences among individuals in the composition of their genes or other DNA sequences

Question 3

WITHOUT GENETIC VARIATION

Answer 3

EVOLUTION CANNOT OCCUR

Question 4

new alleles arise by

Answer 4

mutation, a change in the nucleotide sequence of an organism’s DNA

Question 5

population

Answer 5

a group of individuals of the same species that live in the same area and interbreed, producing fertile offspring

Question 6

gene pool

Answer 6

consists of all copies of every type of allele at every locus in all members of the population

Question 7

“fixed”

Answer 7

if only one allele exists for a particular locus in all members of populations and all individuals will homozygous

Question 8

hardy-weinberg principle

Answer 8

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

Question 9

hardy-weinberg equation

Answer 9

p^2 + 2pq + q^2 = 1

Question 10

conditions for hardy-weinberg equilibrium

Answer 10

1. no mutations
2. random mating
3. no natural selection
4. extremely large population size
5. no gene flow

Question 11

DEPARTURE FROM THESE CONDITIONS

Answer 11

RESULTS IN EVOLUTION

Question 12

natural selection can cause

Answer 12

adaptive evolution, which is evolution that results in a better match between organisms and their environment

Question 13

genetic drift

Answer 13

chance events can also cause allele frequencies to fluctuate unpredictably from on generation to the next, especially in small populations

Question 14

founder effect

Answer 14

when few individuals become isolated from teh larger population, and may establish a new population whose gene pool differs from source population

Question 15

bottleneck effect

Answer 15

sudden change in the environment, fire or flood, may drastically reduce the size of a population

Question 16

effects of genetic drift

Answer 16

1. significant in small populations
2. can cause allele frequencies ro change at random
3. can lead to a loss of genetic variation within populations
4. can cause harmful alleles to become fixed

Question 17

gene flow

Answer 17

transfer of alleles into or out of a population due to movement of fertile individuals or their gametes

Question 18

adaptive evolution

Answer 18

natural selection consistently increases the frequencies of alleles that provide reproductive advantage and thus leads to

Question 19

relative fitness

Answer 19

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

Question 20

directional selection

Answer 20

occurs when conditions favor individuals at one extreme of a phenotypic range, thereby shifting a population’s frequency curve for the phenotypic character in one direction or the other

Question 21

disruptive selection

Answer 21

occurs when conditions favor individuals at both extremes of a phenotypic range over individuals with intermediate phenotypes

Question 22

stabilizing selection

Answer 22

acts against both extreme phenotypes and favors intermediate variants

Question 23

sexual selection

Answer 23

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

Question 24

sexual dimorphism

Answer 24

a difference in secondary sexual characteristics between male and females of the same species. these distinctions include differences in size, color, ornamentation and behavior

Question 25

intrasexual selection

Answer 25

meaning selection within the same sex, individuals of one sex compete directly for mates of the opposite sex. in many species, this occurs between males.

Question 26

intersexual selection

Answer 26

also called mate choice, individuals of one sex (usually females) are choosy in selecting their mates form the other sex. in many cases, female choice depends of the showiness of the male's appearance or behavior

Question 27

neutral variation

Answer 27

differences in DNA sequence that do not confer a selective advantage or disadvantage. but variation is also found at loci affected by selection

Question 28

balancing selection

Answer 28

occurs when natural selection maintains two or more forms in a population

Question 29

heterozygote advantage

Answer 29

if individuals who are heterozygous at a particular locus have greater fitness than do both kinds of homozygotes

Question 30

frequency-dependent selection

Answer 30

the fitness of a phenotype depends on how common it is in the population

Question 31

Why Natural Selection Cannot Fashion Perfect Organisms

Answer 31

1. selection can only act on existing variations 2. evolution is limited by historical constraints 3. adaptations 4. chance, natural selection, and the enviromental interaction