Chapter 7 Quiz

. Natural selection and genetic drift are the two most important causes of evolutionary change. How do they differ?

Only natural selection can change the frequencies of alleles in a population.

Genetic drift is nonadaptive; it changes allele frequency without regard to fitness.

Only genetic drift has been observed in populations of finite size.

Natural selection involves a population moving toward a goal, while genetic drift is not directed.

Natural selection focuses on the survival of individuals, while genetic drift refers to which individuals actually reproduce.

. A large population of three-spined stickleback fish lives in an Alaskan lake. Two alleles segregate at a neutral locus. The allele frequency of the first allele is 0.78. What is the most likely frequency of that allele in the next generation?

0.10

0.50

0.51

0.79

0.90

. Consider a hypothetical locus with several segregating alleles. The population size is small, mutation is absent, and none of the alleles has a selective advantage. Which of the following is likely to occur after a long period of time (many generations)?

Allele frequencies will change over time, but all alleles will remain.

Allele frequencies will remain constant.

Balancing selection will maintain all the alleles.

Allele frequencies will cycle over time.

Genetic variation will decline as alleles randomly go extinct.

. Two alleles segregate at a locus. Assuming that no stabilizing forces exist, the first allele will eventually be

fixed.

either lost or found.

preserved.

either fixed or broken.

either lost or fixed.

. Human mtDNA lineages coalesce to a point about 125,000 years ago in an individual who has been dubbed "Mitochondrial Eve." What does this name mean?

The human population at the time had only one female.

Many females lived at the time, but extant mtDNA is descended from only one of them.

The name "Eve" first appeared in the historical record over 100,000 years ago.

This individual had offspring with "Y-Chromosome Adam," giving rise to modern humans.

There are many origins for modern Homo sapiens.

. "Mitochondrial Eve" is the human female that represents the most recent common ancestor for all human mitochondria; she probably lived about 125,000 years ago in Africa. If we imagine that humans go through a major genetic bottleneck, reducing the population by half, what will become of our conception of Mitochondrial Eve?

Our conception will remain unchanged, as history cannot be re-written.

The designation of Mitochondrial Eve will probably move to a human female that lived more recently, because genes will coalesce less distantly in the past.

We would re-estimate the geographic region that Mitochondrial Eve would have been found in, based on mortality data of the bottleneck.

We would estimate that Mitochondrial Eve would have lived more distantly in the past, with the recognition that humans have gone through many population bottlenecks.

The concept of Mitochondrial Eve would be abandoned, and be replaced by Y-Chromosome Adam.

. Which condition is most likely to account for a difference between the census population size (total number of individuals) and the effective population size (N_e) in a rapidly growing population of humans?

Individuals take long time to reach sexual maturity.

There are different numbers of males and females in the population.

There are frequent matings between full and half-siblings.

Inbreeding is low or nonexistent.

Population size fluctuates.

. In the late eighteenth century, a typhoon swept through the Pacific atoll of Pingelap, leaving approximately 20 survivors. A large percentage of the present-day inhabitants of Pingelap are color blind. One can conclude, therefore, that the population experienced a

coalescence.

speciation event.

selective sweep.

bottleneck.

mutation.

. Which observation would be the best evidence for a recent founder event or population bottleneck?

Census evidence for a steadily growing population

Roughly equal genetic variation in all subregions of a species range

Evidence that a specific genotype has a strong selective advantage in an environment

Evidence that population size on an island is maintained by a steady influx of migrants from the mainland

Low genetic diversity in a single population of a widely distributed species

. Which bit of genetic material would be under the greatest selective constraint?

DNA in the centromere of a chromosome

Nucleotides found at the first position of codons in an intron

A chromosomal region with a high recombination rate

An exon that codes for the active site of a protein enzyme

Second position nucleotides of codons in a pseudogene

. The heterozygosity resulting from drift in an isolated island population of humans is 0.0018. If the neutral mutation rate of 3 × 10^–⁸, predict the effective population size.

556

15,000

60,000

240,000

4,629,629,630

. Which statement about genetic drift is true?

Mildly disadvantageous alleles can sometimes increase in frequency, due to genetic drift.

Evolution by random genetic drift proceeds faster in large populations than in small populations.

Linkage disequilibrium cannot occur, because of genetic drift.

New mutations that are neutral are less likely to be fixed in small populations than in large populations.

Heterozygosity is unaffected by genetic drift.

. Which mutation is most likely to become fixed?

A neutral or nearly neutral mutation in an extremely large population

A beneficial mutation in an extremely large population

A neutral or nearly neutral mutation in an extremely small population

A beneficial mutation in an extremely small population

All of these mutations are equally likely to be fixed.

. A new mutation appears in a population of bears with N_e = 100,000. It provides a selective advantage of 0.015 relative to other genotypes. According to population genetic theory, what is the probability that the mutant allele will achieve fixation?

0.000015

0.001

0.002

0.015

0.030

. Which assumption does not underlie Kimura's neutral theory of molecular evolution?

High amounts of genetic variation segregate in natural populations.

Evolutionary changes at the molecular level occur at a relatively constant rate.

Advantageous mutations occur often, and many fixation events are due to positive selection.

Mutation rates affect rates of substitution.

Deleterious alleles are eliminated by means of (purifying) natural selection.

. The Congo River formed about 1.5 million years ago and has acted as a barrier, preventing interbreeding by chimpanzees (Pan troglodytes) and bonobos (Pan paniscus). If we estimate the mutation rate of their pseudogenes to be 1.9 × 10^–⁵, what is the minimum number of nucleotide differences that we would expect to find in pseudogenes between these two ape species?

14

28

57

114

52,631

. Which observation is not evidence of positive selection in DNA sequences?

Direct observation that individuals with specific alleles leave behind more descendants

A d_N/d_S ratio much greater than one

Clocklike sequence evolution in protein coding genes

A greater d/π ratio at synonymous sites than at nonsynonymous sites

Unusually high sequence divergence in a localized population

Chapter 7 Quiz

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