Chapter 20: Genes Within Populations

in Hardy-Weinberg equilibrium?

1. The population is isolated from other populations of the same species. 2.Allele frequencies are stable from one generation to the next. 3. Genotype frequencies but not phenotype frequencies are the same from one generation to the next.

Which of the following accurately describes sperm competition?

A female mates with multiple males and not every male's sperm has equal chances of fertilizing an egg.

Select all of the following that could cause evolutionary change by natural selection.

A plant with an enzyme that makes it disease-resistant A moth that has a gene for cryptic coloration

Select the observations that would indicate that a population is deviating from Hardy-Weinberg equilibrium.

Allele frequencies are changing between generations. Genotype frequencies do not match those predicated by the Hardy-Weinberg equation based on existing allele frequencies.

Why does selection occur?

Because some individuals in a population possess more favorable phenotypes than others.

Consider a gene that has 4 alleles in a particular population: F, M, S, and VS. What is the sum of all of the frequencies of all the alleles for this gene in that population?

Blank 1: 1, 1.0, or 100%

The processes that lead to evolutionary change are mutations, natural selection,----drift, gene flow and---mating.

Blank 1: genetic or Genetic Blank 2: nonrandom, non-random, or selective

Which type of selection favors individuals at one extreme of a phenotypic range who have greater reproductive success in a particular environment?

Directional selection

Selection against intermediate-sized beaks in African black-bellied seedcracker finches is an example of which of the following?

Disruptive selection

Which type of selection acts to eliminate individuals which are intermediate on a phenotypic range?

Disruptive selection not Directional selection Reason: In directional selection, one of the extremes in the phenotypic range becomes less and less frequent. In this question, it is the intermediate phenotype (not an extreme) that is being eliminated.

What conclusion can be drawn from the observation that a population is not in Hardy-Weinberg equilibrium?

Evolutionary forces are affecting the population.

Which of the following is a driving force of intersexual selection?

Female choice of males based on certain characteristics

what term quantifies reproductive success of a phenotype?

Fitness

Evolutionary change is not caused by phenotypic variation if the phenotypic variation lacks which of the following?

Genetic basis

What evolutionary mechanism results in random changes in allele frequencies from one generation to the next?

Genetic drift

Select all of the following processes that can cause changes in allele or genotype frequencies in populations.

Genetic drift Mutations Gene flow Nonrandom Mating Natural selection

Many 19th century scientists believed that natural selection always favored an optimal form, and therefore would tend to reduce or eliminate which of the following?

Genetic variation

How does natural selection affect allele frequencies?

It causes detrimental alleles to become less common. It causes beneficial alleles to become more common.

How does genetic drift affect allele frequencies?

It changes allele frequencies randomly.

Which of the following statements about the reproductive strategies of males and females is true?

Males and females often have different reproductive strategies.

Evolutionary change within a population can result from which of the following?

Migration Natural selection Mutations

What is the ultimate source of all new alleles?

Mutation

if we find evidence that a population is experiencing changes in allele frequencies from one generation to the next, we say that this population is which of the following?

Not in Hardy-Weinberg equilibrium

Which of the following statements about intrasexual selection (assume males are the competing sex) is true?

Often a few successful males may engage in an inordinate number of matings, while most males do not mate at all.

In Northeastern South America, which of the following is the main predator in streams found just below waterfalls?

Pike cichlids

Choose all the components of fitness from the list below:

Production of viable, numerous offspring Mating success Individual survival

What is genetic drift?

Random changes in the allele frequencies of a population over time

A deer's antlers, a ram's horns and the bright plumage of a male paradise bird are all examples of which of the following?

Secondary sexual characteristics

genetic drift has a greater impact on which of the following?

Small populations

Genetic drift has a greater impact on which of the following?

Smaller Genz

he most fit phenotype produces, on average, which of the following?

The greatest number of surviving offspring

What is gene flow?

The movement of alleles into or out of a population.

The phenotype frequency is calculated by dividing the total number of individuals with a particular phenotype by which of the following?

The total number of individuals in that population

What can likely happen to uncommon alleles in small, isolated populations as a result of genetic drift?

They are likely to be lost

Genetic variation in a population results from evolutionary forces that cause changes in

allele frequencies

in genes that are epistatic in nature,

an allele's selective advantage may vary from one individual to another based on their genotype.

Consider two populations (population A and population B) of the same plant species and the gene Xx. Researchers discover that there is constant flow of the x allele from population B into population A. This allele happens to be detrimental to individuals in population A because of the local soil conditions. In this case gene flow

appears to be constraining evolutionary change.

When researchers raised guppies in laboratory pools with high levels of predation, the guppies in those aquariums

became smaller and drab in coloration as a result of natural selection after about 10 generations.

In many animals, selection has favored traits that confer greater ability in mate competition; as a result of such selection, one of the sexes —usually males—can look very different. This is known as sexual -------

dimorphism

In theory, if mutation rates were high enough, alleles could be maintained in a population

even if the alleles are not favored by natural selection.

in natural populations, most genes

exhibit variation.

Promoting or constraining evolutionary change via the movement of beneficial or detrimental alleles into or out of a population is an effect of

gene flow.

Natural populations exhibit significant phenotypic and ----variation.

genetic or genotypic

Assortative mating changes ______ frequencies but does not change ______ frequencies.

genotype; allele Reason: Nonrandom mating can affect the frequency of heterozygotes.

According to the theory of blending Inheritance, offspring were expected to be phenotypically -----relative to their parents, which would dilute any new genetic variants.

intermediate

Select the types of large populations that are more likely to experience genetic drift.

large population of garter snakes in which only a few individuals contribute to the next generation. A large population of garter snakes that started from a few individuals.

Natural selection

mechanism causes beneficial traits that are heritable to become more common in a population

Changes in allele frequencies / changes in the nucleotide sequences of an organism's DNA

mutations

When a population is in Hardy-Weinberg equilibrium

no natural selection is occurring.

Ground finches with large bills are favored during times of drought, while ground finches with small bills are favored during times when water is abundant. This is an example of

oscillating selection

For a gene with two alleles, what equation represents the sum of all gene frequencies?

p + q = 1

In chickens, the same gene that affects a hen's comb also affects the rate at which the hen lays eggs. Tis is an example of

pleiotropy.

Gene flow may (choose all that apply)

promote evolutionary change. remove alleles from a population. introduce new alleles to a population. reduce evolutionary change.

The amount of genetic variation present in naturally occurring populations is

significant.

In frequency-dependent selection

the fitness of a phenotype depends on its frequency in the population.

New mutations are not a major factor affecting the allele frequencies in a population because

the rate at which new mutations occur is low

For a population to be in Hardy-Weinberg equilibrium

there must be no migration into or out of the population.

s a result of epistasis, the selective advantage of an allele

would vary from one genotype to another.

Which evolutionary mechanism changes genotype frequencies but does not change allele frequencies?

Assortative mating

Select all of the following criteria that must be present for natural selection to occur and cause evolutionary change in a population.

Variation must have a genetic basis. Variation must exist among individuals. Variation must result in differences in the number of offspring surviving in the next generation.