BIOL 1407 - Ch 19

Select all of the following that are true about maintaining genetic variation in populations.

-Evolutionary forces can work in opposition to change allele frequencies. -Evolutionary forces can act together to change allele frequencies.

Choose all the components of fitness from the list below:

-Mating success -Individual survival -Production of viable, numerous offspring

Select reasons why genetic variation within natural populations was a puzzle to Darwin and other scientists in the 19th century.

-Segregation of alleles among progeny of hybrids was not understood. -Scientists thought that selection should always favor an optimal form. -Genetic variants were expected to be diluted to the point of disappearing in future generations.

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

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

Select all of the following factors that limit what selection can accomplish.

-interactions between genes -pleiotropy -lack of genetic variation

Gene flow may

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

Fitness is a measure of

-survival. -number of offspring produced per mating. -mating success.

If the frequency of heterozygotes in a population of mice is 0.48 for a particular gene, what would be the frequency of heterozygotes in future generations if the population is in Hardy-Weinberg equilibrium?

0.48

In what type of selection does a breeder select for desirable characteristics in organisms?

Artificial selection

Why does selection occur?

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

What is the founder effect?

Changes in allele frequencies that result from the colonization of a new location by a small group of individuals from a larger population

Sexual selection is a type of natural selection in which the evolution of certain traits is driven by which of the following types of competition?

Competition for mates

Who mistakenly believed that evolution occurred at an extremely slow pace?

Darwin

What type of selection favors individuals with phenotypes toward one end of an array of phenotypes?

Directional

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

Directional selection

Which of the following types of selection favors extreme forms at both ends of a range of phenotypes?

Disruptive

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

Evolutionary forces are affecting the population.

True or false: When a population is in Hardy-Weinberg equilibrium, natural selection is occurring.

False

What term quantifies reproductive success of a phenotype?

Fitness

In what type of selection is a phenotype favored based on how common or uncommon it is?

Frequency-dependent selection

Which of the following agents of evolutionary change occurs when alleles move from one population to another?

Gene flow

Gene flow can sometimes promote evolutionary change, but at other times it can constrain evolutionary change. How is that possible?

Gene flow can spread a beneficial allele or an inferior allele from one population to other populations.

For natural selection to occur, variation in traits must be which of the following?

Genetic and heritable

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

Genetic drift

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

What did the scientists Godfrey Hardy and Wilhelm Weinberg explain?

Genetic variation in a population

Select the statement that describes nonrandom mating.

Genetically similar individuals preferentially mate with each other.

After Mendel's work was rediscovered, what scientists explained why a population doesn't always come to be composed solely of individuals with the dominant phenotype?

Hardy and Weinberg

In a large population that is not subject to mutation, migration, selection, or nonrandom mating, the proportions of genotypes are stable and the population is said to be in ___-___ equilibrium, named after the scientists who described this principle.

Hardy-Weinberg

Which term describes a situation in which organisms with two different alleles at a particular loci are favored and maintained within a population?

Heterozygote advantage

When heterozygous advantage exists, how would you describe the fitness of the heterozygous genotype?

It has higher fitness than either homozygote

By favoring different phenotypes at different times, oscillating selection acts in which way?

It maintains genetic variation in a population.

Consider a gene with two alleles, one dominant, and the other recessive. If this population is in Hardy-Weinberg equilibrium with respect to this gene, what would happen to the dominant allele from generation to generation?

Its frequency will remain unchanged

What is the ultimate source of all new alleles?

Mutation

___ is the ultimate source of genetic variation.

Mutation

What evolutionary process is occurring if individuals with certain genotypes mate with each other more commonly than would be expected on a random basis?

Nonrandom mating

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

___ selection is a type of natural selection in which competition for mates drives the evolution of certain traits.

Sexual

What type of selection acts to eliminate both extremes from an array of phenotypes?

Stabilizing

___ selection acts to prevent change away from an already common intermediate phenotype.

Stabilizing

Which type of selection favors individuals with intermediate phenotypes and selects against individuals with extreme phenotypes?

Stabilizing selection

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

The greatest number of surviving offspring

How is the size of a population related to the likelihood that the population will experience genetic drift?

The larger the population, the lower the chance of genetic drift is.

What is gene flow?

The movement of alleles into or out of a population.

True or false: Genetic drift could cause an allele that increases fitness to be lost from a population.

True

True or false: Genetic drift, mutations, and nonrandom mating are three agents that can act to produce evolutionary changes in a population.

True

Directional selection

acts to eliminate one extreme from a range of phenotypes.

The bottleneck effect occurs when allele frequencies change due to

an event that drastically reduces population size.

Natural selection favors characteristics that confer a survival advantage because these traits

are also likely to increase the likelihood of reproduction.

Frequency-dependent selection favors phenotypes which ____.

are rare or common

Recent evolutionary studies have shown that Darwin was mistaken in his belief that evolution occurred ____.

at a very slow pace

In artificial selection, the ______ selects individuals with desired characteristics to produce offspring, and in natural selection, the ______ selects which individuals will produce the most offspring.

breeder; environment

Suppose that a population of finches migrates to a small island where most of the seeds are large. On the island, birds with large beaks are more likely to survive, and over time, the mean beak size of the population increases. This is an example of ___ selection.

directional

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.

The word ___ is used to refer to how an entity, such as a species, changes over time.

evolution

The accumulation of differences in species that causes new species to arise from existing ones is a process called

evolution.

If a population is not in Hardy-Weinberg equilibrium, then ___ processes are operating.

evolutionary

In natural populations, most genes

exhibit variation.

Consider two populations of the same plant species - population A and population B 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. This is an example of

gene flow opposing natural selection.

Multiple ___ are usually responsible for most traits.

genes

Random changes in allele frequencies in small populations are known as ___ ___.

genetic drift

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

genetic; nonrandom

Disruptive selection removes ___ phenotypes from a population.

intermediate

A characteristic that confers a survival advantage

is likely to also increase reproductive success and, as a consequence, favored by natural selection.

Most phenotypes in nature are affected by

more than one gene.

Multiple phenotypic effects of alleles, lack of genetic variation, and interactions between genes can all limit what ______ can accomplish.

natural selection

The process in which beneficial traits that are heritable become more common in successive generations is called ____.

natural selection

Darwin proposed that the mechanism of evolution is

natural selection.

If a population is in Hardy-Weinberg equilibrium, then

no new mutations occur.

In a population that is in Hardy-Weinberg equilibrium, proportions of genotypes are

not changing.

In nature, mutation rates are usually ______ to maintain alleles that are not favored in a population by natural selection.

not high enough

A type of natural selection called ___ selection favors different phenotypes at different times and maintains ___ variation in populations.

oscillating; genetic

In the Hardy-Weinberg equation, the allele frequencies of a gene with two alleles are usually represented by ____.

p and q.

If a gene has two alleles R and r, the frequency of the R allele is usually designated as p, and the frequency of the r allele is usually designated as

q.

Sexual selection often results in the evolution of features that increase the chance that a male will be chosen by a female (for example, bright plumage in many male birds); these features are known as ___ ___ characteristic.

secondary sex

The amount of genetic variation present in naturally occurring populations is

significant.

A dramatic reduction in population size due to a natural disaster or destruction of habitat and the resulting change in the allele frequencies of the new population is called

the bottleneck effect.

The change in allele frequencies that occur due to the colonization of a new location by a small group of individuals is called

the founder effect.

Selection occurs because some individuals in a population have more favorable ___ than others in the same population and leave more progeny than others.

traits