23.1 Genetic variation makes evolution possible

Question 1

1) Which of these is a statement that Darwin would have rejected?
A) Environmental change plays a role in evolution.
B) The smallest entity that can evolve is an individual organism.
C) Individuals can acquire new characteristics as they respond to new environments or
situations.
D) Inherited variation in a population is a necessary precondition for natural selection to
operate.
E) Natural populations tend to produce more offspring than the environment can
support.

Answer 1

B) The smallest entity that can evolve is an individual organism.

Question 2

2) Which definition of evolution would have been most foreign to Charles Darwin during his lifetime?
A) change in gene frequency in gene pools
B) descent with modification
C) the gradual change of a populationʹs heritable traits over generations
D) populations becoming better adapted to their environments over the course of
generations
E) the appearance of new varieties and new species with the passage of time

Answer 2

A) change in gene frequency in gene pools

Question 3

3) About which of these did Darwin have a poor understanding?
A) that individuals in a population exhibit a good deal of variation
B) that much of the variation between individuals in a population is inherited
C) the factors that cause individuals in populations to struggle for survival
D) the sources of genetic variations among individuals
E) how a beneficial trait becomes more common in a population over the course of generations

Answer 3

D) the sources of genetic variations among individuals

Question 4

6) Which of these is the smallest unit upon which natural selection directly acts?
A) a speciesʹ gene frequency
B) a populationʹs gene frequency
C) an individualʹs genome
D) an individualʹs genotype
E) an individualʹs phenotype

Answer 4

E) an individualʹs phenotype

Question 4

7) Which of these is the smallest unit that natural selection can change?
A) a speciesʹ gene frequency
B) a populationʹs gene frequency
C) an individualʹs genome
D) an individualʹs genotype
E) an individualʹs phenotype

Answer 4

B) a populationʹs gene frequency

Question 5

4) If, on average, 46% of the loci in a speciesʹ gene pool are heterozygous, then the average homozygosity of the species should be
A) 23%
B) 46%
C) 54%
D) 92%
E) There is not enough information to say .

Answer 5

C) 54%

Question 6

5) Which of these variables is likely to undergo the largest change in value as the result of a mutation that introduces a brand-new allele into a populationʹs gene pool at a locus that had formerly been fixed?
A) Average heterozygosity
B) Nucleotide variability
C) Geographic variability
D) Average number of loci

Answer 6

A) Average heterozygosity

Question 7

8) Which of these evolutionary agents is most consistent at causing populations to become better suited to their environments over the course of generations?
A) Mutation
B) Non-random mating
C) Gene flow
D) Natural selection
E) Genetic drift

Answer 7

D) Natural selection

Question 8

9) Which statement about the beak size of finches on the island of Daphne Major during prolonged drought is true?
A) Each bird evolved a deeper, stronger beak as the drought persisted.
B) Each bird developed a deeper, stronger beak as the drought persisted.
C) Each birdʹs survival was strongly influenced by the depth and strength of its beak as the drought persisted.
D) Each bird that survived the drought produced only offspring with deeper, stronger beaks than seen in the previous generation.
E) The frequency of the strong-beak alleles increased in each bird as the drought persisted.

Answer 8

C) Each birdʹs survival was strongly influenced by the depth and strength of its beak as the drought persisted.

Question 9

10) Each of the following has a better chance of influencing gene frequencies in small populations than in large populations, but which one most consistently requires a small population as a precondition for its occurrence?
A) Mutation
B) Non-random mating
C) Genetic drift
D) Natural selection
E) Gene flow

Answer 9

C) Genetic drift

Question 9

11) In modern terminology, diversity is understood to be a result of genetic variation. Sources of variation for evolution include all of the following except
A) mistakes in translation of structural genes.
B) mistakes in DNA replication.
C) translocations and mistakes in meiosis.
D) recombination at fertilization.
E) recombination by crossing over in meiosis.

Answer 9

A) mistakes in translation of structural genes.

Question 9

12) A trend toward the decrease in the size of plants on the slopes of mountains as altitudes increase is an example of
A) a cline.
B) a bottleneck.
C) relative fitness.
D) genetic drift.
E) geographic variation.

Answer 9

A) a cline.

Question 9

13) The higher the proportion of loci that are ʺfixedʺ in a population, the lower is that populationʹs
A) nucleotide variability.
B) genetic polyploidy.
C) average heterozygosity.
D) A, B, and C
E) A and C only

Answer 9

E) A and C only

Question 10

16) Rank the following 1-base point mutations (from most likely to least likely) with respect to their likelihood of affecting the structure of the corresponding polypeptide:

1. insertion mutation deep within an intron
2. substitution mutation at the 3rd position of an exonic codon
3. substitution mutation at the 2nd position of an exonic codon
4. deletion mutation within the first exon of the gene

A) 1, 2, 3, 4
B) 4, 3, 2, 1
C) 2,1,4,3
D) 3, 1, 4, 2
E) 2, 3, 1, 4

Answer 10

B) 4, 3, 2, 1

Question 11

17) Sponges are known to contain a single Hox gene. Most invertebrates have a cluster of 10 similar Hox genes, all located on the same chromosome. Most vertebrates have four such clusters of Hox genes, located on four non-homologous chromosomes. The process responsible for the change in number of Hox genes from sponges to invertebrates was most likely __________, whereas a different process that could have potentially contributed to the clusterʹs presence on more than one chromosome was __________.
I. binary fission
II. translation
III. geneduplication IV. non-disjunction V. transcription

A) I, II
B) II, III
C) II, V
D) III, IV
E) III, V

Answer 11

D) III, IV

Question 12

HIVʹs genome of RNA includes code for reverse transcriptase (RT), an enzyme that acts early in infection to synthesize a DNA genome off of an RNA template. The HIV genome also codes for protease (PR), an enzyme that acts later in infection by cutting long viral polyproteins into smaller, functional proteins. Both RT and PR represent potential targets for antiretroviral drugs. Drugs called nucleoside analogs (NA) act against RT, whereas drugs called protease inhibitors (PI) act against PR.

18) Which of these represents the treatment option that is most likely to avoid the production of drug-resistant HIV (assuming no drug interactions or side effects)?

A) using a series of NAs, one at a time, and changed about once a week
B) using a single PI, but slowly increasing the dosage over the course of a week
C) using high doses of NA and a PI at the same time for a period not to exceed 1 day
D) using moderate doses of NA and of two different PIʹs at the same time for several month

Answer 12

D) using moderate doses of NA and of two different PIʹs at the same time for several months

Question 13

HIVʹs genome of RNA includes code for reverse transcriptase (RT), an enzyme that acts early in infection to synthesize a DNA genome off of an RNA template. The HIV genome also codes for protease (PR), an enzyme that acts later in infection by cutting long viral polyproteins into smaller, functional proteins. Both RT and PR represent potential targets for antiretroviral drugs. Drugs called nucleoside analogs (NA) act against RT, whereas drugs called protease inhibitors (PI) act against PR.

19) Within the body of an HIV-infected individual who is being treated with a single NA, and whose HIV particles are currently vulnerable to this NA, which of these situations can increase the virusʹ relative fitness?
1. mutations resulting in RTs with decreased rates of nucleotide mismatch
2. mutations resulting in RTs with increased rates of nucleotide mismatch 3. mutations resulting in RTs that have proofreading capability
A) 1 only
B) 2 only
C) 3 only
D) 1 and 3
E) 2 and 3

Answer 13

B) 2 only

Question 14

HIVʹs genome of RNA includes code for reverse transcriptase (RT), an enzyme that acts early in infection to synthesize a DNA genome off of an RNA template. The HIV genome also codes for protease (PR), an enzyme that acts later in infection by cutting long viral polyproteins into smaller, functional proteins. Both RT and PR represent potential targets for antiretroviral drugs. Drugs called nucleoside analogs (NA) act against RT, whereas drugs called protease
inhibitors (PI) act against PR.

20) HIV has 9 genes in its RNA genome. Every HIV particle contains two RNA molecules, each molecule containing all 9 genes. If, for some reason, the two RNA molecules within a single HIV particle do not have identical sequences, then which of these terms can be applied due to the existence of the non-identical regions?

A) homozygous
B) gene variability
C) nucleotide variability
D) average heterozygosity
E) all except A

Answer 14

E) all except A

Question 15

21) If two genes from one RNA molecule become detached and then, as a unit, get attached to one end of the other RNA molecule within a single HIV particle, which of these is true?

A) There are now fewer genes within the viral particle.
B) There are now more genes within the viral particle.
C) A point substitution mutation has occurred in the retroviral genome.
D) The retroviral equivalent of crossing-over has occurred, no doubt resulting in a heightened positive effect.
E) One of the RNA molecules has experienced gene duplication as the result of translocation.

Answer 15

E) One of the RNA molecules has experienced gene duplication as the result of
translocation.

Question 16

22) The DNA polymerases of all cellular organisms have proofreading capability. This capability tends to reduce the introduction of

A) extra genes by gene duplication events.
B) chromosomal translocation.
C) genetic variation by mutations.
D) proofreading capability into prokaryotes.

Answer 16

C) genetic variation by mutations.

Question 17

23) Which of these makes determining the evolutionary relatedness of different species based on the amino acid sequence of homologous proteins generally less accurate than determinations of relatedness based on the nucleotide sequences of homologous genes?
A) Silent mutations
B) Gene duplications
C) Translocation events that change gene sequences
D) Crossing-over
E) Independent assortment

Answer 17

A) Silent mutations