Chapter 4 - Evolution of Populations

Question 1

Genetic variation in a population results from:

Answer 1

• Mutations form new alleles
• Chromosomal rearrangement
• Gene duplication
• Sexual reproduction

Question 2

Crossing over during meiosis I (prophase I)
Effect:

Answer 2

creates new combinations of genes in the gametes that are not found in either parent, contributing to genetic diversity.

Question 3

Random assortment during meiosis I (metaphase I)
Effect:

Answer 3

produces many variations among daughter cells, giving rise to genetic diversity in offspring.

Question 4

Random fertilization

Answer 4

any egg (with its unique combination of alleles) can be fertilized by any sperm (with its unique combination of alleles).

Question 5

Hardy-Weinberg Equilibrium

Answer 5

• No evolution
• is a mathematical formula that calculates the genotype and phenotype of a population. In a large population mating at random allele frequencies will remain constant if there is no mutation, migration, or natural selection
• What is its significance? identifies variables that can influence evolution in real-world populations.
• Natural populations can evolve at some gene loci while being in Hardy-Weinberg equilibrium at other loci

Question 6

Conditions for Hardy-Weinberg Equilibrium

Answer 6

 No mutation
 No gene flow
 Random mating
 Very large population
 No selection

Question 7

Allele Frequency Equation

Answer 7

p + q = 1
freq. of A freq. of a

Question 8

Genotype Frequencies Equation

Answer 8

p2 + 2pq + q2 = 1
freq. of AA freq. of Aa freq. of aa

Question 9

Mechanisms Of Evolution

Answer 9

• Mutation
• Gene Flow (migration or emigration)
• Non-random mating
• Genetic Drift
• Natural Selection

Question 10

Mutation

Answer 10

 random change in an organism’s DNA that creates a new allele.
 The ultimate source of variation. Individual mutations occur so rarely that mutation alone usually does not change allele frequency much.

Question 11

Gene Flow (migration or emigration)

Answer 11

 exchange of genes from one population to another will contribute to microevolution. A population might gain genes due to migration into the existing population. A population might lose genes due to emigration from the existing population.
 A very potent agent of change. Individuals or gametes move from one population to another.

Question 12

Non-random mating

Answer 12

 inbreeding is the most common form. It does not alter allele frequency but reduces the proportion of heterozygotes.

Question 13

Genetic Drift

Answer 13

 Statistical accidents. The random fluctuation in allele frequencies increases as population size decreases.- change in the gene pool of a large population by chance.
- variation in the relative frequency of different genotypes in a small population, owing to the chance disappearance of particular genes as individuals die or do not reproduce.

Question 14

Natural Selection

Answer 14

 The only agent that produces adaptive evolutionary changes.
- Increases frequencies of alleles that provide reproductive advantage (higher relative fitness)
- genetic drift, mutation, and gene flow lead to microevolution, but it doesn’t necessarily lead to adaptive. Only natural selection is adaptive!
- Natural Selection favors the fittest individuals so they can pass down their alleles to their offspring so the alleles for the fittest phenotype increase over time i.e., the population evolved
- Increases frequencies of alleles that provide reproductive advantage (higher relative fitness)
- 3 conditions:
 Variation in population
 Variation must be genetically inherited
 Variation must result in certain phenotype(s) producing more surviving offspring in following generation

Question 15

Small population effect

Answer 15

In any generation, by chance, some individuals did not get reproduced.

Question 16

Founder effect

Answer 16

o colonization of a new location by a few individuals of a population. The gene pool has been reduced because only a few individuals make up the population.
o Allele frequencies different in founder population

Question 17

Bottleneck effect

Answer 17

o is an event that non-selectively reduces a large population into a small population.

Question 18

3 modes of Natural selection

Answer 18

 Directional selection
 Disruptive selection
 Stabilizing selection

Question 19

Directional selection

Answer 19

phenotypes at one extreme have selective advantage over the rest

Question 20

Disruptive selection

Answer 20

diversifying, both extremes of phenotype are favored over the intermediate.

Question 21

Stabilizing selection

Answer 21

average phenotype has a selective advantage

Question 22

Balancing selection can maintain variation in a population

Answer 22

• e.g., Heterozygote advantage
• e.g., frequency-dependent selection

Question 23

Sexual Selection

Answer 23

• Can lead to sexual dimorphism - distinct difference in size or appearance between the sexes of an animal in addition to differences between the sexual organs themselves.

Question 24

Evolutionary forces can interact

Answer 24

• E.g., natural selection and genetic drift
• E.g., natural selection and gene flow

Question 25

Remember:

Answer 25

- There are limits to what natural selection can accomplish  Why?? Selection can only operate on the available genetic variation. It is not guided by a consciousness; it has no foresight and can lead species to evolve down paths that seem advantageous but actually lead to extinction - There is no “goal” in evolution