19: The Evolution of Populations

Question 1

What is allele frequency?

Answer 1

The rate at which a specific allele appears within a population. AKA gene frequency.

Question 2

What is the founder effect?

Answer 2

An event that initiates an allele frequency change in part of the population, which is not typical of the original population. The founder effect occurs when the genetic structure changes to match that of the new population’s founding fathers and mothers.

Question 3

What is a gene pool?

Answer 3

All of the alleles carried by all of the individuals in the population.

Question 4

What is genetic structure?

Answer 4

The distribution of the different possible genotypes in a population.

Question 5

What is macroevolution?

Answer 5

Broader scale evolutionary changes seen over paleontological time.

Question 6

What is microevolution?

Answer 6

Changes in a population’s genetic structure.

Question 7

What is modern synthesis?

Answer 7

The overarching evolutionary paradigm reconciling Charles Darwin’s theory of evolution and Gregor Mendel’s theory of heredity that took shape by the 1940s and is generally accepted today.

Question 8

What is population genetics?

Answer 8

The study of how selective forces change the allele frequencies in a population over time.

Question 9

What is genetic drift?

Answer 9

The effect of change on a population’s gene pool. Small populations are more susceptible to genetic drift.

Question 10

What is the Hardy-Weinberg principle?

Answer 10

A theory that states that a population’s allele and genotype frequencies are inherently stable - unless some kind of evolutionary force is acting upon the population, neither the allele nor the genotypic frequencies would change. It was proposed by English mathematician Godfrey Hardy and German physician Wilhelm Weinberg in the early 20th century.

Question 11

What is assortative mating?

Answer 11

When individuals tend to mate with those who are phenotypically similar to themselves.

Question 12

What is the bottleneck effect?

Answer 12

Magnification of genetic drift as a result of natural events or catastrophes.

Question 13

What is a cline?

Answer 13

Gradual geographic variation across an ecological gradient.

Question 14

What is gene flow?

Answer 14

The flow of alleles in and out of a population due to the migration of individuals or gametes.

Question 15

What is genetic variance?

Answer 15

Diversity of alleles and genotypes in a population.

Question 16

What is geographical variation?

Answer 16

Differences in the phenotypic variation between populations that are separated geographically.

Question 17

What is heritability?

Answer 17

The fraction of population variation that can be attributed to its genetic variance.

Question 18

What is inbreeding?

Answer 18

Mating of closely related individuals.

Question 19

What is an inbreeding depression?

Answer 19

Increase in abnormalities and disease in inbreeding populations. This can occur because of the combination of deleterious recessive mutations.

Question 20

What is nonrandom mating?

Answer 20

Changes in a population’s gene pool due to mate choice or other forces that cause individuals to mate with certain phenotypes more than others.

Question 21

What is population variation?

Answer 21

Distribution of phenotypes in a population.

Question 22

What is selective pressure?

Answer 22

An environmental factor that causes one phenotype to be better than another.

Question 23

What is an example of the founder effect in human societies?

Answer 23

The founder effect is believed to have been a key factor in the genetic history of the Afrikaner population of Dutch settlers in South Africa, as evidenced by mutations that are common in Afrikaners but rare in most other populations. This is likely due to the fact that a higher-than-normal proportion of the founding colonists carried these mutations. As a result, the population expresses unusually high incidences of Huntington’s disease (HD) and Fanconi anemia (FA), a genetic disorder known to cause blood marrow and congenital abnormalities, including cancer.

Question 24

What are some examples of gene flow?

Answer 24

Many plants send their pollen over distances via wind or birds, and the developing males of a pride of lions leave to seek out a new pride with genetically unrelated females.

Question 25

What is temperature-dependent sex determination (TSD)?

Answer 25

A type of environmental sex determination in which the temperatures experienced during embryonic/larval development determine the sex of the offspring.

Question 26

What is an example of temperature-dependent sex determination?

Answer 26

The sex of the American alligator (Alligator mississippiensis) is determined by TSD. Eggs incubated at 30° C produced females, and eggs incubated at 33° C produce males.

Question 27

What is an example of latitudinal cline?

Answer 27

Species of warm-blooded animals tend to have larger bodies in the cooler climates closer to the earth’s poles, allowing them to better conserve heat.

Question 28

What is an example of altitudinal cline?

Answer 28

Flowering plants tend to bloom at different times depending on where they are along the slope of a mountain.

Question 29

What is adaptive evolution?

Answer 29

An increase in the frequency of beneficial alleles and decrease in deleterious alleles due to selection.

Question 30

What is directional selection?

Answer 30

Selection that favors phenotypes at one end of the spectrum of existing variation.

Question 31

What is diversifying selection?

Answer 31

Selection that favors two or more distinct phenotypes.

Question 32

What is evolutionary fitness?

Answer 32

An individual’s ability to survive and reproduce. AKA Darwinian fitness.

Question 33

What is frequency-dependent selection?

Answer 33

Selection that favors phenotypes that are either common (positive frequency-dependent selection) or rare (negative frequency-dependent selection).

Question 34

What is the good genes hypothesis?

Answer 34

A theory of sexual selection that argues that individuals develop impressive ornaments to show off their efficient metabolism or ability to fight disease.

Question 35

What is the handicap principle?

Answer 35

A theory of sexual selection that argues that only the fittest individuals can afford costly traits.

Question 36

What is an honest signal?

Answer 36

A trait that gives a truthful impression of an individual’s fitness. Both the handicap principle and good genes hypothesis are said to be honest signals of a male’s quality.

Question 37

What is relative fitness?

Answer 37

An individual’s ability to survive and reproduce relative to the rest of the population.

Question 38

What is sexual dimorphism?

Answer 38

A phenotypic difference between the males and females of a population. Often, reproductively successful males are larger and better ornamented.

Question 39

What is stabilizing selection?

Answer 39

Selection that favors average phenotypes.

Question 40

What is an example of stabilizing selection?

Answer 40

Mice whose coat blends in with the forest floor because they are less likely to be spotted by predators.

Question 41

What is an example of directional selection?

Answer 41

Moths in areas with heavy pollution favoring darker colors rather than the otherwise normal lighter colors.

Question 42

What is an example of diversifying selection?

Answer 42

Alpha males that are big and dominate a harem, and “sneaking” males that can steal furtive copulations with the females. Medium-sized males that are too small for alpha and too big to sneak will not be selected for.

Question 43

What is an example of frequency-dependent selection?

Answer 43

An example is the common side-blotched lizard of the Pacific Northwest. There are three variations of throat-color patterns: orange, blue, and yellow. Orange are the strongest and best fighters, blue forms strong pair bonds with mates, and yellow are small but sneaky. Orange can beat off blue to steal mates, blue can successfully guard against yellow sneaks, and yellow can sneak in copulations from orange. Hence, the populations cycle, depending on the prevalence of male type in a given generation.

Question 44

What is an example of the handicap principle?

Answer 44

Peacocks with large tails are slower and easier to spot by predators, hence only the best males survive the risk.