Chapter 5 Quiz

. Which statement about natural selection is true?

It is the same as evolution.

It always results in reduced genetic variation.

It can have an evolutionary effect only if phenotypic differences are heritable.

It acts directly on genotypes.

Changes in allele frequencies can occur only because of natural selection.

. Why did industrial melanism in the peppered moth, Biston betularia, help convince researchers that the intensity of natural selection can be very strong?

The dark-colored morph drove the light-colored morph to extinction.

Birds were unable to prey on the moths once they acquired their color adaptations.

The moth population exploded, covering England with moths during the Industrial Revolution.

The dark-colored allele increased in frequency very rapidly in multiple populations and later decreased rapidly after the environment changed.

Natural selection maintained constant proportions of the color alleles in the population, despite rapid environmental change brought about by the Industrial Revolution.

. Refer to the graph showing the proportion of warfarin-resistant rats in a population of rats in Wales.

According to the graph

there was no selection for warfarin resistance at any time.

there was positive selection against warfarin-resistant rats during all time points.

positive selection for warfarin resistance occurred during the warfarin poisoning program, but rats that were not resistant to warfarin increased in frequency after the poisoning program ended.

selection against warfarin resistance was relaxed during the early part of 1976.

there was positive selection for warfarin resistance at all times.

. Which conditions are required for natural selection to occur?
1. Traits are heritable; offspring resemble parents
2. Traits are coded for by dominant genes
3. Traits are correlated with fitness
4. Populations reproduce sexually

1, 2 and 3

3 and 4

2, 3 and 4

1 and 3

All of the conditions

. Which of the following is the definition of fitness, according to evolutionary biology?

The quality of being able to fulfill a particular role or task

The fecundity of a genotype

The condition of being physically fit and healthy

The viability of a genotype

The average, lifetime contribution of individuals with a particular genotype to a population

. A change in which variable would not necessarily change an organism's fitness?

Mating success

Fertilization success

Fecundity

Mutation rate

Viability

. A population carries two alleles at a locus. One allele has a miniscule fitness advantage. What is the long-term fate of the locus if natural selection is the only important evolutionary force?

Eventually the beneficial allele will be fixed by natural selection.

Both alleles will remain in the population at a ratio proportional to the fitness difference.

The population size will increase.

The population size will decrease.

The allele at a disadvantage will mutate to improve to the fitness level of the other allele.

. In a scenario where a population is evolving only in response to natural selection, allele frequencies will change at a rate proportional to the selection coefficient and the

size of the population.

population's growth rate.

level of genetic variation at the locus.

mean fitness of the population.

degree of the allele's penetrance.

. A new mutation in a population of birds appears. It gives individuals a slight advantage in spotting predators and a fitness advantage. If those that have the mutation have 0.5% greater fitness than those without, what is the probability that the mutation will spread and eventually become fixed?

0.5%

1%

2%

100%

Not enough information is given to answer the question.

. What will happen to DNA sequence variation in the regions of the genome immediately adjacent to an allele undergoing a selective sweep, or strong positive selection?

Decreased variation and high levels of linkage disequilibrium at nearby sites

Increased variation and high levels of linkage disequilibrium at nearby sites

Increased variation and the absence of linkage disequilibrium at nearby sites

Decreased variation and the absence of linkage disequilibrium at nearby sites

No change in local genetic variation

. The colors of individuals in a snail population are determined by a single autosomal locus. A₁A₁ homozygotes are red, A₁A₂ heterozygotes are pink, and A₂A₂ homozygotes are white. Genotypic fitnesses are as follows:

w_{A_{1} A_{1}} = 0.5; w_{A_{1} A_{2}} = 1.0; w_{A_{2} A_{2}} = 0.75 .

At equilibrium,

both alleles are equally frequent.

both alleles are maintained in the population, and allele A₁ is more common than allele A₂.

the population is fixed for allele A₂.

the population contains only A₁A₂ heterozygotes.

both alleles are maintained in the population, and allele A₂ is more common than allele A₁.

. If one genotype in a genetically variable population is favored in dry years and a different genotype is favored in wet years,

genetic variation is not necessarily maintained.

genetic drift will be a stronger force than selection.

genetic variation is always maintained.

rates of fixation are likely to speed up.

hard selection is likely to occur.

. Human sex ratios are close to equal because if one sex becomes rare, it will be at a fitness advantage and increase in frequency in the population until equilibrium at 50:50 is regained. This is an example of

overdominance, or heterozygote advantage.

negative frequency-dependent selection.

positive selection on sex ratio.

underdominance, or heterozygote disadvantage

positive frequency-dependent selection.

. Populations of the grasshopper Vandiemenella viatica possess different chromosomal fusions and inversions. Grasshoppers that are heterozygous for different chromosomal rearrangements have reduced fitness. What would you expect to observe if you investigated the genotypes of grasshoppers in a recently merged population?

New combinations of genes yielding genotypes of greater fitness

Few heterozygotes because of underdominance

Frequency-dependent selection, leading to fluctuations in fitness

Heterozygotes with greater fitness, owing to overdominance

A random assortment of genotypes because of genetic drift

. The end result of positive frequency-dependent selection for a population depends strongly on

the sex ratio of the population.

the initial frequencies of alleles in the population.

the level of background selection.

underdominance by heterozygotes.

the height of the adaptive peak.

. Sewall Wright's metaphor of an "adaptive landscape" that includes "peaks" and "valleys" is used widely in evolutionary biology. Natural selection will always move populations' mean fitness up the peaks. Which influence is most likely to cause a population to move away from a fitness peak towards a valley?

Purifying selection

Large population size

Overdominant selection

Positive selection

Genetic drift

. Consider a deleterious recessive allele that is lethal when homozygous. If the mutation rate at this locus is 10^–⁶, the equilibrium allele frequency will be

0.

0.000001.

0.00001.

0.001.

1.

Chapter 5 Quiz

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