Chapter 20

Question 1

Genetic Variation and Evolution

Answer 1

Genetic variation​

Differences in alleles of genes found within individuals in a population.​

Natural populations contain much variation.​

Evolution​

How an entity changes through time.​

Development of modern concept traced to Darwin.​

“Descent with modification”.

Question 2

Natural selection can

Answer 2

lead to change in allele frequencies

Question 3

Population genetics

Answer 3

Study of properties of genes in a population

Question 4

Genetic variation

Answer 4

Genetic variation in populations now measured using increasingly sophisticated tools

Question 5

S N Ps

Answer 5

Used to assess patterns in over 300 species​

> 100,000 human genomes partially or wholly sequenced

Question 6

Blending inheritance

Answer 6

offspring expected to be phenotypically intermediate relative to parents

Question 7

Hardy–Weinberg principle

Answer 7

Predicts genotype frequencies

Question 8

Hardy–Weinberg equilibrium​

Answer 8

Proportions of genotypes do not change in a population as long as:​

No mutation takes place​

No genes are transferred to or from other sources (no immigration or emigration)​

Mating is random​

The population size is very large​

No selection occurs​

Question 9

Hardy–Weinberg principle equation

Answer 9

Frequency of first allele is p, second allele is q​

p + q = 1 in a population
p^2 + 2pq + q^2 = 1

Question 10

What makes populations vary from Hardy-Weinberg equilibrium?​

Answer 10

Natural selection might favor homozygotes over heterozygotes.​

Individuals may choose to mate with genetically similar individuals.​

Influx of individuals from other populations​

Mutations occurring

Question 11

Agents of evolutionary change

Answer 11

Mutation​

Rates generally low​

Other evolutionary processes usually more important in changing allele frequency​

Ultimate source of genetic variation​

Makes evolution possible​

Gene flow​

Movement of alleles from one population to another​

Animal physically moves into new population​

Drifting of gametes or immature stages of plants or animals into an area​

Pollen and seeds can travel long distances​

Question 12

More Agents of evolutionary change

Answer 12

Nonrandom mating​

Assortative mating​

Phenotypically similar individuals mate​

Increases proportion of homozygous individuals​

Disassortative mating​

Phenotypically different individuals mate​

Produces excess of heterozygotes

Question 13

Genetic drift

Answer 13

Genetic drift​

In small populations, allele frequency may change by chance alone.​

Population must be large to be in H-W equilibrium.​

Magnitude of genetic drift is inversely related to population size.​

Can lead to the loss of alleles in isolated populations and uncommon alleles are more vulnerable.​

Founder effect​

Bottleneck effect

Question 14

Founder effect

Answer 14

One or a few individuals disperse and become the founders of a new, isolated population

Question 15

Bottleneck effect

Answer 15

Drastic reduction in population size due to drought, disease, other natural forces

Question 16

Artificial selection

Answer 16

breeder selects desired characteristics​

Question 17

Natural selection

Answer 17

environmental conditions determine which individuals produce the most offspring

Question 18

Evolution by natural selection conditions

Answer 18

Variation must exist among individuals in a population​

Variation among individuals must result in differences in the number of offspring surviving in the next generation​

Variation must have a genetic basis

Question 19

Fitness

Answer 19

Individuals with one phenotype leave more surviving offspring in the next generation than individuals with an alternative phenotype.

Question 20

Measuring fitness​

Answer 20

Most fit phenotype is assigned fitness value of 1

Question 21

Many components of fitness

Answer 21

Survival​

Sexual selection – some individuals more successful at attracting mates​

Number of offspring per mating​

Traits favored for one component may be a disadvantage for others

Question 22

Parental Investment

Answer 22

Refers to the energy and time each sex invests in producing and rearing offspring

Question 23

Intrasexual selection

Answer 23

competitive interactions between members of one sex

Question 24

Intersexual selection

Answer 24

mate choice

Question 25

Secondary sexual characteristics

Answer 25

antlers and horns used to combat other males; long tail feathers and bright plumage used to “persuade” members of opposite sex

Question 26

Sexual dimorphism

Answer 26

Differences between sexes

Question 27

Sperm competition

Answer 27

selects for features that increase probability that a male’s sperm will fertilize the eggs​

Question 28

Sensory Exploitation

Answer 28

evolution in males of a signal that exploits preexisting biases

Question 29

Frequency-dependent selection

Answer 29

Fitness of a phenotype depends on its frequency within the population.

Question 30

Negative frequency-dependent selection​

Answer 30

Rare phenotypes favored by selection

Question 31

Positive frequency-dependent selection​

Answer 31

Favors common form

Question 32

Oscillating selection

Answer 32

Selection favors one phenotype at one time and another phenotype at another time

Question 33

Heterozygote advantage

Answer 33

Heterozygotes are favored over homozygotes​

Works to maintain both alleles in the population​

Question 34

Disruptive selection​

Answer 34

Acts to eliminate intermediate types​

Question 35

Directional selection

Answer 35

Acts to eliminate one extreme

Question 36

Stabilizing selection

Answer 36

Acts to eliminate both extremes

Question 37

Gene flow can be

Answer 37

Constructive​

Spread beneficial mutation to other populations.​

Constraining​

Can impede adaptation by continual flow of inferior alleles from other populations.