Chapter 23 The Evolution of Populations

Question 1

Genetic Variation

Answer 1

Difference among individuals in the composition of their genes or other DNA segments.

Question 2

Average Heterozygosity

Answer 2

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

Question 3

Geographic Variation

Answer 3

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

Question 4

Cline

Answer 4

A graded change in a character along a geographic axis.

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

The aggregate of all copies of every type of allele at all loci in every individual in a population. The term is also used in a more restricted sense as the aggregate of alleles for just one or a few loci in a population.

Question 7

Hardy-Weinberg Principle

Answer 7

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 8

Five Conditions for HW Equilibrium

Answer 8

1. No Mutations.
2. Random Mating.
3. No natural selection.
4. Extremely Large Population size.
5. No Gene Flow.

Question 9

Genetic Drift

Answer 9

A process in which chance events cause unpredictable fluctuations in allele frequencies from one generation to the next. Effects of genetic drift are most pronounced in small populations.

Question 10

Founder Effect

Answer 10

Genetic drift that occurs when a few individuals become isolated from a larger population and form a new population whose gene pool composition is not reflective of that of the original population.

Question 11

Bottleneck Effect

Answer 11

Genetic drift that occurs when the size of a population is reduced, as by a natural disaster or human actions. Typically, the surviving population is no longer genetically representative of the original population.

Question 12

Genetic Drift Key Points

Answer 12

1. Genetic drift is significant in small populations.
2. Can cause allele frequencies to change at random.
3. Can lead to a loss of genetic variations within populations.
4. Can cause harmful alleles to become fixed.

Question 13

Gene Flow

Answer 13

The transfer of alleles from one population to another, resulting from the movement of fertile individuals or their gametes.

Question 14

Relative Fitness

Answer 14

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

Question 15

Directional Selection

Answer 15

Natural Selection in which individuals at one end of the phenotypic range survive or reproduce more successfully than do other individuals.

Question 16

Disruptive Selection

Answer 16

Natural selection in which individuals on both extremes of a phenotypic range survive or reproduce more successfully than do individuals with intermediate phenotypes.

Question 17

Stabilizing Selection

Answer 17

Natural selection in which intermediate phenotypes survive or reproduce more successfully than do extreme phenotypes.

Question 18

Sexual Selection

Answer 18

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

Question 19

Sexual Dimorphism

Answer 19

Differences between the secondary sex characteristics of males and females.

Question 20

Intrasexual Selection

Answer 20

Selection in which there is direct competition among individuals of one sex for mates of the opposite sex.

Question 21

Intersexual Selection

Answer 21

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 22

Balancing Selection

Answer 22

Natural selection that maintains two or more phenotypic forms in a population.

Question 23

Heterozygote Advantage

Answer 23

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

Question 24

Frequency-Dependent Selection

Answer 24

Selection in which the fitness of a phenotype depends on how common the phenotype is in a population.