Ch. 26

Question 1

A gene pool is..

Answer 1

All of the genes in a population of individuals

Question 2

In natural populations, most genes are..

Answer 2

Polymorphic

Question 3

A gene exists in two alleles designated D and d. If 48 copies of this gene are the D allele and 152 are the d allele, what is the allele frequency of D?

Answer 3

Total = 200
40/200 = .24

Question 4

The allele frequency of C is 0.4 and c is 0.6. If the population is in Hardy-Weinberg equilibrium, what is the frequency of heterozygotes?

Answer 4

2pq = 2(0.6)(0.4) = .48

Question 5

Which of the following is a factor that does NOT promote widespread changes in allele or genotype frequencies?
A) new mutations
B) natural selection
C) genetic drift 
D) migration
E) nonrandom mating

Answer 5

A) New mutations

Question 6

Darwinian fitness is a measure of..

Answer 6

Reproductive success

Question 7

Within a particular population, darkly colored rats are more likely to survive than more lightly colored individuals. This scenario is likely to result in ___ ___.

Answer 7

Directional selection

Question 8

A population occupies a diverse environment in which the fitness of some genotypes is higher in one environment while the fitness of other individuals is higher in another environment. This scenario is likely to result in ___ ___.

Answer 8

Disruptive selection

Question 9

A gene exists in two alleles, and the heterozygote has the highest fitness. This scenario is likely to result in ___ ___.

Answer 9

Balancing selection

Question 10

What does the term “local population” mean?

Answer 10

A local population is a group of individuals that are more likely to interbreed with each other compared with more distant populations

Question 11

Are polymorphisms common or rare in natural populations?

Answer 11

Polymorphisms are very common in nearly all natural populations

Question 12

Directional selection

In this form of natural selection, explain the meaning of the word “directional.”

Answer 12

The word “directional” means that selection is favoring a particular phenotype.

Selection is moving the population in the direction in which that phenotype will predominate.

Question 13

Directional selection for DDT resistance in a mosquito population.

In this example, is directional selection promoting genetic diversity? Explain.

Answer 13

No, because directional selection is eliminating individuals that are sensitive to DDT.

Question 14

The geographic relationship between malaria and the frequency of the sickle cell allele in human populations.

Explain why the Hb^5 allele is prevalent in certain regions even though it is detrimental in the homozygous condition.

Answer 14

The Hb^5 allele is an advantage in the heterozygous condition because it confers resistance to malaria. The heterozygote advantage outweighs the homozygote disadvantage.

Question 15

Explain how negative frequency-dependent selection works.

Answer 15

In negative frequency-dependent selection, the rarer phenotype has a higher fitness, which improves its reproductive success.

Question 16

Disruptive selection.

Does this form of natural selection favor polymorphism? Explain why or why not.

Answer 16

Yes, this selection favors polymorphism. The fitness values of phenotypes depend on the environment. Some phenotypes are the fittest in one environment whereas other phenotypes are the fittest in another environment.

Question 17

Stabilizing selection.

In general, why does stabilizing selection decrease genetic diversity?

Answer 17

Stabilizing selection decreases genetic diversity because it eliminates individuals that carry alleles that promote more extreme phenotypes.

Question 18

The central issue in ___ ___ is genetic variation.

Answer 18

Population genetics

Question 19

Population genetics

It’s foundations are largely attributed to 3 mathematicians:

Answer 19

• sir Ronald fisher
• sewall wright
• J. B. S. Haldane

Question 20

All of the alleles of every gene in a population make up the ___ ___.

Answer 20

Gene pool

Question 21

The focus is shifted away from the individual and toward..

Answer 21

The population of which the individual is a member

Question 22

Only individuals that ___ contribute to the gene pool of the next generation.

Answer 22

Reproduce

Question 23

Population geneticists study..

Answer 23

The genetic variation within the gene pool and how it changes from one generation to the next

Question 24

A ___ is a group of individuals of the same species that occupy the same region and can interbreed with each other.

Answer 24

Population

Question 25

A large population is usually composed of smaller groups called ___ ___, or “___.”

Answer 25

Local populations, demes

Question 26

Local populations are often separated from each other by moderate ___ ___.

Answer 26

Geographic barriers

Question 27

A population may change in:

Answer 27

• size
• geographic location
• genetic composition

Question 28

The term ___ refers to the observation that many traits display variation within a population with the gene existing as two or more allele.

Answer 28

Polymorphism

Question 29

At the DNA level, polymorphism is due to..

Answer 29

Two or more alleles that influence the phenotype

Question 30

“___” is also used to describe a gene that commonly exists as 2 or more alleles in a population.

Answer 30

Polymorphic

Question 31

A ___ gene exists predominately as a single allele.

Answer 31

Monomorphic

Question 32

Variation can even be as small as ___ ___ ___.

Answer 32

Single-nucleotide polymorphism (SNP)

Question 33

Allele frequency=

Answer 33

of copies of an allele in a population/ total # of all alleles for that gene in a population

Question 34

Genotypes frequency=

Answer 34

of individuals with a particular genotype in a population / total # of individuals in a population

Question 35

The HW equation is also called an ___.

Answer 35

Equilibrium

Question 36

The HW equation provides a quantitative relationship between the ___ and ___ ___.

Answer 36

Alleles and genotype frequencies

Question 37

If the chi square is too high, we would say the population is in ___.

Answer 37

Disequilibrium

Question 38

___ describes changes in a populations gene pool from generation to generation.

Answer 38

Microevolution