Deck 1: Genetics of Bacteria and Bacteriophages

Question 1

For which trait is human mating expected to be nonrandom?

A) Skin color
B) Isocitrate dehydrogenase enzyme
C) Blood type
D) Hair color
E) Fingerprint loci

Answer 1

A

Question 2

A sizable population was analyzed for SNPs in a certain DNA region and found all four possible variants at the following frequencies: SNP 1: GGTCTAGGA; frequency = 0.91 SNP 2: GGTGTAGGA; frequency = 0.03 SNP 3: GGTATAGGA; frequency = 0.03 SNP 4: GGTTTAGGA; frequency = 0.03 What is the total frequency of heterozygotes at this SNP locus?

A) 0.009
B) 0.0018
C) 0.170
D) 0.828
E) 0.055

Answer 2

C

Question 3

In the Hardy-Weinberg model, the ideal population is

A) free of mutations.
B) randomly mating.
C) non-migrating.
D) very large.
E) all of the above.

Answer 3

E

Question 4

________ is the ultimate source of genetic variation in populations.

A) Natural selection
B) Gene flow
C) Recombination
D) Mutation
E) Genetic drift

Question 5

If the genotypic frequencies for an allele in an HW population are 0.635 homozygous dominants, 0.430 heterozygotes, and 0.125 homozygous recessives, what is the frequency of the recessive allele?

A) 0.65
B) 0.01
C) 0.125
D) 0.875
E) 0.35

Question 6

For a gene A, a geneticist studying a population of beetles found the following genotypes: AA 45 beetles Aa 347 beetles aa 8 beetles What is the observed genotypic frequency of Aa individuals?

A) 1.15
B) 0.02
C) 0.13
D) 0.90
E) 0.86

Question 7

In reciprocal hybrid crosses, the heterogametic sex is typically sterile while the homogametic sex is not. This phenomenon is now called

A) male sterility.
B) hybrid incompatibility.
C) Haldane's rule.
D) postzygotic isolation.
E) None of the above

Question 8

Sterile offspring of hybrid matings provide an example of

A) prezygotic isolation.
B) sexual selection.
C) postzygotic isolation.
D) natural selection.
E) heterosis.

Question 9

In the absence of gene flow, two populations are expected to

A) change genetically in parallel fashion.
B) become gradually dissimilar over time.
C) experience different degrees of genetic drift.
D) experience different mutation rates.
E) remain identical owing to natural selection.

Question 10

Twenty loci are screened for genetic variation in a common caterpillar species. Four loci are found to have two or more alleles. The proportion of polymorphic loci for this population is thus

A) 0.10.
B) 0.20.
C) 0.30.
D) 0.40.
E) 0.50.

Question 11

Which of the following is not a form of genetic drift?

A) Founder event
B) Population bottleneck
C) Heterozygote advantage
D) Nonrandom mating
E) All of the above are forms of genetic drift.

Question 12

In the Hardy-Weinberg model, the frequency of heterozygotes is represented as

A) p2.
B) p.
C) 2pq.
D) q.
E) q2.

Question 13

Genetic drift may lead to

A) increased heterozygosity at many loci.
B) a decrease in the mutation rate of a particular gene.
C) loss of genetic variation in a population.
D) Hardy-Weinberg equilibrium.
E) all of the above.

Question 14

Which method is least useful for assessing levels of genetic variation in populations?

A) Phenotypic observation
B) DNA sequencing
C) VNTRs
D) Protein electrophoresis
E) RFLP analysis

Question 15

The balance model of genetic variation proposes that

A) levels of genetic variation are determined by a balance between genetic drift and gene flow.
B) natural selection maintains genetic variation in populations.
C) most individuals in a population will be homozygous for alleles favored by natural selection.
D) recurrent mutation and random processes maintain variation without natural selection.
E) alleles that function best are strongly favored by natural selection.

Question 16

What is the frequency of the a allele in the beetle population described in question 14?

A) 0.91
B) 0.55
C) 0.86
D) 0.09
E) 0.45

Question 17

Heterozygotes for the sickle-cell allele show higher fitness than either homozygote genotype in malarial regions. This is an example of

A) heterosis.
B) codominance.
C) founder effect.
D) epistasis.
E) pleiotropy.

Question 18

For two populations to remain genetically homogenized, a significant proportion of the population of each must be exchanged at least every other generation.

Question 19

Conservation geneticists are interested in assessing the smallest sustainable population size for species of concern. Such studies are called

A) population variation analysis.
B) minimum stable population analysis.
C) outbreeding threshold analysis.
D) population viability analysis.
E) inbreeding threshold analysis.

Question 20

Which of the following populations would be expected to experience the greatest degree of genetic drift?

A) Oak trees in the Great Smoky Mountains National Park
B) White-tailed deer in the eastern U.S.
C) Wild pandas
D) Rat populations in New York City
E) Canada geese

Question 21

Mutation may be the ultimate source of genetic variation, but sexual reproduction and similar processes like bacterial conjugation or transformation are also important in continually generating novel genetic combinations.

Question 22

In the early twentieth century, evolutionary biologists argued whether there was enough genetic variation in populations to explain the diversity of life by natural selection. With the advent of protein electrophoresis and DNA-level analysis, the problem turned on its head: the neutralist school arose from the idea that there was too much genetic variation to be maintained by natural selection. What are some of the arguments and observations neutralists cited to support the idea that much variation is neither favored nor disfavored by natural selection?

Question 23

According to the Hardy-Weinberg principle, at equilibrium the allele frequencies are dependent on the genotypic frequencies.

Question 24

Two neighboring Caribbean islands harbor iguana populations. One island (island

Question 25

Two populations experience equally severe bottlenecks, reducing each to one-tenth their original size. One population is in the bottleneck for one generation, and the other is in the bottleneck for five generations. You assess heterozygosity of both populations after they have been restored to their prebottleneck size. What do you expect to find, and why?

Question 26

The deciduous forest of eastern North America experienced dramatic changes over the past two to three centuries, transitioning from a nearly continuous forested area to increasingly patchy forest broken up by farming and development. Some species are more sensitive to severe habitat fragmentation than others; what are some characteristics that might make a species more susceptible to the effects of habitat and population fragmentation?

Question 27

A selection coefficient of 1 means zero fitness.

Question 28

Observed genotypic frequencies in populations rarely match HW expectations exactly. Why is this so, and how can you determine if the frequencies you observe depart from HW in a biologically meaningful degree?

Question 29

Why do we expect that postzygotic isolation evolutionarily precedes prezygotic isolation in the speciation process?

Question 30

The population mean for a given measured trait is observed to decline over the course of several generations. This is an example of disruptive selection.

Question 31

Some recessive mutations can be exceedingly debilitating or lethal when expressed in homozygotes. If their effects are so severe, why doesn't natural selection simply purge such alleles from the population completely?

Question 32

Two closely related insect species are active at different times of day, with one diurnal and the other nocturnal. This is an example of spatial isolation.

Question 33

The northern elephant seal, Mirounga angustirostris, suffered a significant population bottleneck in the late nineteenth century, when hunting reduced their population size to as few as 20 individuals. It has since rebounded to several tens of thousands. The related southern elephant seal, M. leonine, was not hunted as intensively. What prediction can you make about the relative levels of heterozygosity in populations of these two species?

Question 34

With respect to a gene with two alleles, for each generation of complete inbreeding the proportion of heterozygotes is expected to be reduced by 1/2 while the proportion of each homozygous class is expected to increase in frequency by 1/4. Explain why this is so.

Question 35

In light of the fact that the assumptions of the Hardy-Weinberg principle are unrealistic (no mutation, no selection, etc.), how can the principle be useful to population geneticists?

Question 36

Show algebraically that under Hardy-Weinberg equilibrium, allele frequencies will not change from one generation to another.

Question 37

Populations that suffer significant reductions in number may experience two population-genetic consequences that together can hasten their decline. Which two processes are likely to act in concert in small populations, and what is their effect?

Question 38

The frequency of a recessive X-linked allele is equal to the phenotypic frequency of males exhibiting that allele.

Question 39

Survival is the single most important process in evolution by natural selection.

Question 40

The Hardy-Weinberg relationship cannot be used to compute allele frequencies when one or more alleles are recessive.

Question 41

This chapter discussed speciation by genetic divergence following geographic isolation, which is expected to lead to reduced gene flow. This is known as allopatric speciation. A more controversial form of speciation is genetic divergence of populations without physical isolation; this is called sympatric speciation. Can you envision a mechanism or process that would permit two coexisting populations of the same species to begin to diverge without being isolated from one another?

Question 42

Remote oceanic islands are characterized as having disharmonic biota, meaning the number and relative proportions of taxa living on the island differ significantly from the number and relative proportions of taxa on the nearest continental mainland area. Each island system is disharmonic in its own unique way. Why?