Question 1

Which of these evolutionary agents is most consistent at causing populations to become better suited to their environments over the course of generations?

Accepted Answer

Natural selection is the most consistent evolutionary agent that leads to the gradual adaptation of populations to their environments over the course of generations. This is because natural selection favors individuals with beneficial traits that increase their survival and reproductive success, leading to an accumulation of advantageous traits in the population over time. In contrast, mutation, non-random mating, gene flow, and genetic drift can all contribute to changes in the genetic makeup of a population, but they do not necessarily lead to an overall increase in adaptation to the environment.

Question 2

Which definition of evolution would have been most foreign to Charles Darwin during his lifetime?

Accepted Answer

During Darwin's lifetime, the concept of genes and gene frequency was not yet understood or discovered. The idea of evolution as a change in gene frequency in gene pools would have been foreign to him.

Question 3

Which of these is the smallest unit that natural selection can change?

Accepted Answer

Natural selection acts on populations by changing the frequency of genes within the population over generations.

Question 4

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 cluster's presence on more than one chromosome was __________. I. binary fission
II. translation
III. gene duplication
IV. non-disjunction
V. transcription

Accepted Answer

The process responsible for the change in number of Hox genes from sponges to invertebrates was most likely gene duplication. This is because the cluster of 10 similar Hox genes in invertebrates suggests that an ancestral Hox gene underwent duplication, resulting in multiple similar genes on the same chromosome. A different process that could have potentially contributed to the cluster's presence on more than one chromosome was non-disjunction. Non-disjunction can result in chromosomes that have an abnormal number of genes, which could contribute to the clustering of Hox genes on multiple chromosomes in vertebrates.

Question 5

Use the following information to answer the questions below.
HIV's 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.
-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)?

Accepted Answer

Using moderate doses of NA and two different PIs simultaneously for several months is likely to be most effective in preventing drug resistance. This combination therapy, known as Highly Active Antiretroviral Therapy (HAART), targets multiple stages of the viral life cycle, reducing the chance of the virus developing resistance.

Question 6

Use the following information to answer the questions below.
HIV's 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.
-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 virus' 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

Accepted Answer

If the HIV particles are vulnerable to a single NA, which acts against RT, then mutations resulting in RTs with increased rates of nucleotide mismatch can increase the virus' relative fitness. This is because these mutations may introduce errors that enable the virus to escape the effects of the NA. Mutations resulting in RTs with decreased rates of nucleotide mismatch would not provide an advantage in this situation. Mutations resulting in RTs that have proofreading capability would also not provide an advantage, as this would decrease the rate of mutations and slow down the virus' ability to evolve and adapt to changing conditions.

Question 7

A trend toward the decrease in the size of plants on the slopes of mountains as altitudes increase is an example of

Accepted Answer

A cline refers to a gradual change in a characteristic of a population as one moves geographically through different environments. In this case, the trend toward smaller plant size as altitude increases is a cline as the environment (in this case, altitude) gradually changes. The other answer choices (bottleneck, relative fitness, genetic drift, geographic variation) do not accurately describe this specific example.

Question 8

In modern terminology, diversity is understood to be a result of genetic variation. Sources of variation for evolution include all of the following except

Accepted Answer

Mistakes in translation of structural genes do not result in genetic variation since they do not change the DNA sequence. Genetic variation arises from changes in the DNA sequence itself, which can occur through mistakes in DNA replication, translocations and mistakes in meiosis, recombination at fertilization, and crossing over in meiosis.

Question 9

Which of these is the smallest unit upon which natural selection directly acts?

Accepted Answer

Natural selection acts directly on an individual's phenotype, which is the physical expression of their genotype. In other words, it is the observable trait or characteristic of an individual that influences their ability to survive and reproduce. The other options (A-C) refer to gene frequency at larger scales, and (D) refers to the specific genetic makeup of an individual, which can influence their phenotype but is not directly acted upon by natural selection.

Question 10

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 population's gene pool at a locus that had formerly been fixed?

Accepted Answer

Average heterozygosity is a measure of the proportion of individuals in a population that are heterozygous at a particular locus. If a new allele is introduced into a population's gene pool, it is likely to increase the number of heterozygous individuals, and therefore increase the average heterozygosity. Nucleotide variability and geographic variability are measures of differences between populations and are less likely to be affected by a single allele introduction. The average number of loci is a fixed value and is not affected by changes in individual alleles.

Question 11

If, on average, 46% of the loci in a species' gene pool are heterozygous, then the average homozygosity of the species should be

Accepted Answer

If 46% of loci are heterozygous, then the remaining loci must be homozygous: 
100% - 46% = 54% homozygous 
Therefore, the average homozygosity of the species should be 54%.

Question 12

Which statement about the beak size of finches on the island of Daphne Major during prolonged drought is True?

Accepted Answer

During the drought, finches with deeper, stronger beaks were more likely to survive because they could access the limited food resources, influencing survival based on beak characteristics.

Question 13

Use the following information to answer the questions below.
HIV's 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.
-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?

Accepted Answer

The presence of non-identical sequences in the RNA molecules of an HIV particle indicates variability at the nucleotide level, which can be described by terms like gene variability and nucleotide variability. Average heterozygosity is also a measure of genetic variation, so all options except homozygous (which implies identical sequences) are applicable.

Question 14

About which of these did Darwin have a poor understanding?

Accepted Answer

While Darwin had observed that individuals exhibit variation and recognized that this variation can be inherited, he did not have a complete understanding of the sources of genetic variation among individuals. It wasn't until the discovery of genetics and the work of scientists such as Gregor Mendel that the mechanisms underlying inheritance and genetic variation were better understood.

Question 15

Which statement about variation is True?

Accepted Answer

New alleles arise from changes in the nucleotide sequence, which is nucleotide variability.

Question 16

Which of these is a statement that Darwin would have rejected?

Accepted Answer

Darwin's theory of evolution by natural selection requires variation to exist within a population, and the smallest unit of evolution is the population, not an individual organism. While individual organisms can adapt to new environments, the adaptation is not genetic and cannot be passed down to future generations. Darwin would not have rejected the other statements.

Question 17

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?

Accepted Answer

Genetic drift is the random fluctuation of allele frequencies in a population due to chance events. This effect is more pronounced in small populations, where chance events can have a greater impact on the gene pool. Therefore, genetic drift consistently requires a small population as a precondition for its occurrence. While the other options can also have a greater impact on gene frequencies in small populations, they do not necessarily require a small population as a precondition.

Question 18

The higher the proportion of loci that are "fixed" in a population, the lower is that population's

Accepted Answer

When loci are "fixed," there is no variation at those genetic sites, leading to lower nucleotide variability and average heterozygosity.

Question 19

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

Accepted Answer

A deletion mutation within the first exon (4) is most likely to affect the polypeptide structure as it can cause a frameshift. A substitution at the 2nd position (3) often changes the amino acid, affecting the protein. A substitution at the 3rd position (2) may be silent due to codon redundancy. An insertion within an intron (1) is least likely to affect the polypeptide as introns are non-coding regions.

Question 20

In a hypothetical population's gene pool, an autosomal gene, which had previously been fixed, undergoes a mutation that introduces a new allele, one inherited according to incomplete dominance. Natural selection then causes stabilizing selection at this locus. Consequently, what should happen over the course of many generations?

Accepted Answer

Stabilizing selection favors the heterozygous state and opposes both homozygous genotypes. Therefore, over time, both types of homozygotes should decrease in frequency, while the proportion of the population that is heterozygous should increase. This will lead to an increase in the population's average heterozygosity. Therefore, the correct choice is (E), both (A) and (C).

Quiz 23: The Evolution of Populations