Mechanisms of Evolution

Question 1

gene pool

Answer 1

All of the alleles of all of the genes in a certain population.

Question 2

Hardy-Weinberg principle

Answer 2

A principle of population genetics stating that genotype frequencies in a large population do not change from generation to generation in the absence of evolutionary processes

Question 3

What are the key assumptions of the Hardy-Weinberg model?

Answer 3

1) No natural selection at the gene in question
2) No genetic drift, or random allele frequency changes, affecting the gene in question
3) No gene flow
4) No mutation
5) Random mating with respect to the gene in question

Question 4

When does the Hardy-Weinberg principle serve as a null hypothesis?

Answer 4

When biologists want to test whether natural selection is acting on a particular gene, non random mating is occurring, or any of the evolutionary mechanisms are at work

Question 5

genetic variation

Answer 5

(1) The number and relative frequency of alleles present in a particular population. (2) The proportion of phenotypic variation in a trait that is due to genetic rather than environmental influences in a certain population in a certain environment.

Question 6

directional selection

Answer 6

A pattern of natural selection that favors one extreme phenotype with the result that the average phenotype of a population changes in one direction. Generally reduces overall genetic variation in a population

Question 7

purifying selection

Answer 7

Selection that lowers the frequency or even eliminates deleterious alleles.

Question 8

stabilizing selection

Answer 8

A pattern of natural selection that favors phenotypes near the middle of the range of phenotypic variation. Reduces overall genetic variation in a population.

Question 9

disruptive selection

Answer 9

–has a role in speciation

Question 10

heterozygote advantage

Answer 10

A pattern of natural selection that favors heterozygous individuals compared with homozygotes. Tends to maintain genetic variation in a population.

Question 11

balancing selection

Answer 11

A pattern of natural selection in which no single allele is favored in all populations of a species at all times. Instead, there is a balance among alleles in terms of fitness and frequency.

Question 12

frequency-dependent selection

Answer 12

A pattern of selection in which certain alleles are favored only when they are rare; a form of balancing selection.

Question 13

genetic drift

Answer 13

Any change in allele frequencies due to random events. Causes allele frequencies to drift up and down randomly over time, and eventually can lead to the fixation or loss of alleles.

Question 14

sampling error

Answer 14

The accidental selection of a nonrepresentative sample from some larger population, due to chance.

Question 15

What are some key points concerning genetic drift?

Answer 15

• is random with respect to fitness
• is most pronounced in small populations
• over time genetic drift can lead to random loss or fixation of alleles

Question 16

founder effect

Answer 16

A change in allele frequencies that often occurs when a new population is established from a small group of individuals (founder event) due to sampling error (i.e., the small group is not a representative sample of the source population).

Question 17

Genetic bottleneck

Answer 17

A reduction in allelic diversity resulting from a sudden reduction in the size of a large population (population bottleneck) due to a random event.

Question 18

gene flow

Answer 18

The movement of alleles between populations; occurs when individuals leave one population, join another, and breed.

Question 19

mutation

Answer 19

Any change in the hereditary material of an organism (DNA in most organisms, RNA in some viruses)

Question 20

deletrious

Answer 20

In genetics, referring to any mutation or allele that reduces an individual’s fitness.

Question 21

beneficial

Answer 21

In genetics, referring to any mutation, allele, or trait that increases an individual’s fitness.

Question 22

What are the key roles of mutation in evolution?

Answer 22

• Mutation ultimate source of genetic variation
• if mutation did not occur, evolution would eventually stop
• mutation alone is inconsequential in changing allele frequencies at a particular gene

Question 23

inbreeding

Answer 23

Mating between closely related individuals. Increases homozygosity of a population and often leads to a decline in the average fitness

Question 24

What are the key points of inbreeding?

Answer 24

• inbreeding increases homozygosity

- inbreeding does not cause evolution, because allele frequencies do not change in the population as a whole

Question 25

inbreeding depression

Answer 25

In inbred offspring, fitness declines due to deleterious recessive alleles that are homozygous.

Question 26

Does inbreeding speed the rate of evolutionary change?

Answer 26

Yes it increases rate at which purifying selection eliminates recessive deleterious alleles from the population

Question 27

sexual selection

Answer 27

A pattern of natural selection that favors individuals with traits that increase their ability to obtain mates. Acts more strongly on males than females.

Question 28

sexual selection acts more strongly on males or females?

Answer 28

Males

Question 29

Territory

Answer 29

An area that is actively defended by an animal from others of its species.

Question 30

Sexual dimorphism

Answer 30

Any trait that differs between males and females.