Chapter 23: Evolution of Populations

Question 1

Microevolution

Answer 1

Evolutionary change within populations that results from changes in allele frequencies over generations

Question 2

Gene variability

Answer 2

Genetic variation at the whole gene level that can be quantified as the average percentage of loci that are heterozygous

Question 3

Neutral variation

Answer 3

Differences in DNA sequence that do not confer a selective advangtage or disadvantage

Question 4

Sources of genetic variation

Answer 4

1. Formation of new alleles via mutations
2. Chromosomal changes that alter gene number or position
3. Rapid reporduction; increases frequency of mutaitons
4. Sexual reproduction; genetic shuffling that results from crossing-over, independent assortment of chromosomes, and random fertilization

Question 5

Population

Answer 5

A group of individuals of the same species that live in the same area and interbreed to produce fertile offspring

Question 6

Gene pool

Answer 6

The genetic makeup of a population that consists of all copies of every type of allele at every locus in all members of a population

If only one allele exists for a particular locus in a population the allele is fixed and all individuals in the population are homozygous for that alllele

Question 7

Hardy-Weinberg equilibrium

Answer 7

State where a population is not evolving; allele and genotype frequencies remain constant from generation or generation

Question 8

Conditions for the Hardy-Weinberg equilibrium

Answer 8

Question 9

Mechanisms that directly alter allele frequencies and cause most evolutionary change

Answer 9

1. Natural selection
2. Genetic drift
3. Gene flow

Question 10

Adaptive evolution

Answer 10

Traits that enhance survival or reporduction tend to increase in frequency over time

Question 11

Gentic drift

Answer 11

Chance events that cause allele frequencies to fluctuate unpredictable from one generation to the next

• Effects can be significant in small populations
• Can cause allele frequencies to change at random
• Can lead to a loss of genetic variation within populations
• Can cause harmful alleles to become fixed

Question 12

Founder effect

Answer 12

Type of genetic drift

When a few individuals become isolated from a larger population they may have a develop a gene pool that differs from the source population

Question 13

Bottleneck effect

Answer 13

Type of genetic drift

When a severe drop in a population alters the gene pool by random chance, leads some alleles to be more or less represented than they were in the original population

Question 14

Gene flow

Answer 14

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

Question 15

Relative fitness

Answer 15

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

Question 16

Ways natural selection can alter gene distribution

Answer 16

Directional selection- occurs when conditions favor individuals exhibiting one extreme of a phenotypic range; shifts character in one direction or another

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

Stabilizing selection- acts against both extreme phenotypic variants; favors intermediate phenotypes

Question 17

Sexual selection

Answer 17

Process in which individuals with certain inherited characteristics are more likely than other individuals of the same sex to obtain mates

Can result in sexual dimorphism- a difference in secondary sex characteristics between males and females of the same species

Question 18

Intrasexual selection

Answer 18

Selection that acts on individuals of the same sex where they directly compete for a mate

Question 19

Intersexual selection

Answer 19

Individuals of one sex are choosy in selecting their mates from the other sex; mate choice

Often, females chose males based off the showiness of the male’s appearance or behavior

Question 20

Balancing selection

Answer 20

Selection itself may preserve variation at some loci, thus maintain-
ing two or more phenotypic forms in a population

Frequency-dependent selection- the fitness of a phenotype depends on how common it is in the population

Heterozygote advantage- individuals who are heterozygous have a greater fitness than those who are homozygous in terms of genotype

Question 21

Limitations of natural selection

Answer 21

1. Selection can only act on existing variations currently in the population
2. Evolution is limited by historical constraints; builds on past structures
3. Adaptations are a compromise between positive and negative consequences
4. Environmental variation alters what traits are best suited to a given time or place