26: Evolutionary Processes

Question 1

genetic drift

Answer 1

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 2

gene flow

Answer 2

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

Question 3

mutation

Answer 3

Any change in the hereditary material of an organism (DNA in most organisms, RNA in some viruses). The only source of new alleles in populations.

Question 4

Hardy-Weinberg principle

Answer 4

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 (e.g., mutation, gene flow, genetic drift, and selection), and nonrandom mating.

Question 5

inbreeding

Answer 5

Mating between closely related individuals. Increases homozygosity of a population and often leads to a decline in the average fitness via selection (inbreeding depression).

Question 6

deleterious

Answer 6

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

Question 7

inbreeding depression

Answer 7

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

Question 8

sexual selection

Answer 8

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

Question 9

genetic variation

Answer 9

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

Question 10

directional selection

Answer 10

A mode 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 11

purifying selection

Answer 11

Selection that lowers the frequency of or even eliminates deleterious alleles.

Question 12

stabilizing selection

Answer 12

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

Question 13

disruptive selection

Answer 13

A mode of natural selection that favors extreme phenotypes at both ends of the range of phenotypic variation. Maintains overall genetic variation in a population.

Question 14

balancing selection

Answer 14

A mode 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 15

heterozygote advantage

Answer 15

A pattern of natural selection favors heterozygous individuals compared with homozygotes. Tends to maintain genetic variation in a population, thus is a form of balancing selection.

Question 16

frequency dependent selection

Answer 16

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

Question 17

intersexual selection

Answer 17

The sexual selection of an individual of one gender for mating by an individual of other gender (usually by female choice).

Question 18

intrasexual selection

Answer 18

Competition among members of one gender for an opportunity to mate (usually male-male competition).

Question 19

territory

Answer 19

An area that is actively defended by an animal from others of its species and that provides exclusive or semi-exclusive use of its resources by the owner.

Question 20

sexual dimorphism

Answer 20

Any trait that differs between males and females.

Question 21

ecological selection

Answer 21

Also known as environmental selection. A type of natural selection that favors individuals with heritable traits that enhance their ability to survive and reproduce in a certain physical and/or biological environment, excluding their ability to obtain a mate.

Question 22

sampling error

Answer 22

The selection of a non representative sample from some larger population, due to chance.

Question 23

genetic marker

Answer 23

A genetic locus that can be identified and traced in populations by laboratory techniques or by a distinctive visible phenotype.

Question 24

genetic bottleneck

Answer 24

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 25

beneficial

Answer 25

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

Question 26

Natural selection

Answer 26

Increases the frequency of certain alleles–the ones that contribute to reproductive success in a particular environment. It is the only one of the four processes that leads to adaptation.

Question 27

Four processes that can shift allele frequencies in populations over time, causing evolution:

Answer 27

Natural selection, genetic drift, gene flow, and mutation.