Connect Ch. 20

In a population of seahorses, red seahorses on average produce 125 offspring and brown seahorses produce 75 offspring. What is the fitness of the brown phenotype?

0.6

When quantifying fitness in natural populations, the most fit phenotype is assigned a fitness value of ______.

1

What would indicate that a population is deviating from Hardy-Weinberg equilibrium.

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

Which evolutionary mechanism does not change allele frequencies, but changes genotype frequencies by increasing the proportion of homozygotes in the next generation?

Assortative mating

Why does selection occur?

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

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

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

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 true of evolutionary forces in natural populations?

Evolutionary forces can alter allele frequencies in natural populations.

True or false: Within the same species, females and males usually employ the same reproductive strategy.

False

What term quantifies reproductive success of a phenotype?

Fitness

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

Gene flow

What processes that can cause changes in allele or genotype frequencies in populations?

Genetic drift, Gene flow, Mutations, Natural selection, and Nonrandom Mating

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

Genetic variation

How does genetic drift affect allele frequencies?

It changes allele frequencies randomly.

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

It maintains genetic variation in a population.

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

Males and females often have different reproductive strategies.

What is true about the reproductive strategies of males and females?

Males are selective in choosing a mate much less frequently than females.

Evolutionary change within a population can result from which of the following? (3)

Natural selection, Migration, and Mutations

What conditions that must be met for a population to be in Hardy-Weinberg equilibrium?

No new mutations occur, Mating is random, The population is very large.

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

Pike cichlids

What type of selection affects traits that influence an individual's chances to find a mating partner or be chosen as a mating partner?

Sexual selection

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

Stabilizing selection

Which of the following statements describes frequency-dependent selection?

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

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

The greatest number of surviving offspring

What appears to determine variations in the coloration, size and maturation of guppies in northeastern South American streams?

The location of streams relative to waterfalls

What is gene flow?

The movement of alleles into or out of a population.

What is fitness?

The relative likelihood that a genotype will contribute to the gene pool of the next generation

In a laboratory experiment, researchers placed guppies in three different types of pools: no predation, low predation, and high predation. Researchers hypothesized that predation is a selective force and that large, brightly colored guppies are more conspicuous to predators. Based on that, what would you predict the guppies will look like in the pool with high predation after 10 generations?

They should be smaller and not very brightly colored.

What 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 result in differences in the number of offspring surviving in the next generation, and Variation must exist among individuals.

The term heterozygote ___ refers to situations in which heterozygotes are more fit then either homozygotes.

advantage

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

____ selection favors individuals at one extreme of a phenotypic range. Those individuals usually have greater reproductive success in a particular environment.

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

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

Genetic variation is necessary for ___ change to occur.

evolutionary

In natural populations, most genes ______.

exhibit variation

In general, ___ are more likely to exhibit mate choice than...

females; males

In ___ - ___ , selection, the fitness of a phenotype depends on the proportion of individuals in the population that have that phenotype.

frequency-dependent.

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

Evolution can result from any process that changes the ______ composition of a population.

genetic

Evolutionary change cannot occur in populations when there is no ___ variation.

genetic

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

genetic; nonrandom

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

genotype; allele

Consider a gene with two alleles, A1 and A2. If the fitness of A1A2 individuals is higher than the fitness of both A1A1 and A2A2, we are observing ______.

heterozygote advantage

according to the theory of blending inheritance, offspring were expected to be phenotypically ______ relative to their parents, which confused scientists originally because variation would be diluted

intermediate

Hardy-Weinberg equilibrium requires that the population size is ___ and that mating is ___.

large; random

Sexual selection influences ______.

mating success, fitness, and mate choice

What is the ultimate source of all new alleles?

mutation

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

not high enough

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

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

pleiotropy

Gene flow may (choose all that apply)

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

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

sexual

The amount of genetic variation present in naturally occurring populations is ______.

significant

Genetic drift has a greater impact on what size population?

small

___ selection favors individuals with intermediate phenotypes and selects against individuals with extreme phenotypes.

stabilizing

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

As a result of epistasis, the selective advantage of an allele ______.

would vary from one genotype to another