Question 1

The idea of relative fitness is best exemplified in which of the following statements?
A) A deer that teaches her offspring how to avoid predators has a higher relative fitness than a deer that does not teach her offspring to avoid predators.
B) A flowering plant that attracts fewer bees that transfer pollen to other plants has higher relative fitness than a plant that attracts more pollen-transferring bees.
C) A bison that does not digest grasses efficiently has a higher relative fitness than a bison that has more efficient digestion.
D) An oak seedling that always dies when infected with a certain virus has higher relative fitness than an oak seedling that always survives the infection

Accepted Answer

Relative fitness refers to the ability of an organism to pass on its genes to the next generation in comparison to other organisms. A deer teaching its offspring to avoid predators increases the offspring's survival chances, thereby increasing the deer's relative fitness by ensuring its genes are passed on more effectively.

Question 2

A proficient engineer can easily design skeletal structures that are more functional than those currently found in the forelimbs of such diverse mammals as horses, whales, and bats. Which of the following statements best explains why the actual forelimbs of these mammals do not seem to be optimally arranged?
A) Natural selection has not had sufficient time to create the optimal design in each case, but will do so given enough time.
B) In many cases, phenotype is determined by genotype and the environment.
C) Although we may not consider the fit between the current skeletal arrangements and their functions excellent, we should not doubt that natural selection ultimately produces the best design.
D) Natural selection is generally limited to modifying structures that were present in previous generations and in previous species.

Accepted Answer

Natural selection works by modifying existing structures rather than creating new ones from scratch, which explains why the current forelimbs of these mammals may not seem optimally arranged according to human engineering standards.

Question 3

Imagine a small herbaceous flowering plant whose conservation status is "endangered." Which of the following possible experiments would best test if a lack of genetic variability was partially responsible for low population numbers?
A) compare flower production rates in plants from populations that occur in dry versus moist conditions
B) compare flower production rates in small versus large plants
C) compare seed production rates in plants that are hand-pollinated with pollen from nearby individuals versus individuals 10 kilometers away
D) compare seed production rates in small versus large plants

Accepted Answer

Comparing seed production rates in plants that are hand-pollinated with pollen from nearby individuals versus individuals 10 kilometers away directly tests the effect of genetic variability on reproductive success. If plants pollinated with distant (potentially more genetically diverse) pollen produce more seeds, it suggests that genetic variability (or lack thereof) affects population numbers.

Question 4

When a species deviates from a 50:50 sex ratio (male to female), the members of the minority sex often receive a greater proportion of care and resources from parents than do the offspring of the majority sex. Which of the following processes most likely causes this pattern?
A) sexual selection
B) balancing selection
C) stabilizing selection
D) frequency-dependent selection

Accepted Answer

This pattern is most likely caused by frequency-dependent selection, where the fitness of a phenotype depends on its frequency relative to other phenotypes in the population. In this case, the rarity of one sex makes it more valuable for reproductive success, leading parents to invest more resources in offspring of the minority sex to maximize their own genetic contribution to future generations.

Question 5

Which of the following statements about evolutionary forces is accurate?
A) Unlike the other evolutionary forces, gene flow is the only force that causes populations to become more different.
B) Unlike the other evolutionary forces, mutation is the only force that decreases genetic variability.
C) Unlike the other evolutionary forces, nonrandom mating is the only force that changes allele frequency.
D) Unlike the other evolutionary forces, natural selection is the only force that improves the match between the organism and its environment.

Accepted Answer

Natural selection is unique among evolutionary forces in that it consistently works to improve the adaptation of organisms to their environment by favoring alleles that increase survival and reproductive success. Gene flow tends to homogenize populations, mutation increases genetic variability, and nonrandom mating affects the distribution of genotypes but does not directly change allele frequencies.

Question 6

Imagine a human population with an extremely low frequency of sickle cell alleles. Which of the following changes is most likely in the human population 15 generations after introducing a mosquito population that carries the malaria parasite?
A) an increase in red blood cells without nuclei
B) a decrease in the number of mosquito bites
C) an increase in the mutation rate of the hemoglobin gene
D) an increase in the sickle cell allele

Accepted Answer

The sickle cell allele provides a selective advantage in malaria-endemic areas because individuals with one copy of the allele (heterozygotes) have increased resistance to malaria. Over generations, this can lead to an increase in the frequency of the sickle cell allele in a population exposed to malaria.

Question 7

Adult male humans generally have deeper voices than do adult female humans. Which of the following processes was most likely occurring given that the fossil records of apes and humans alike show a trend toward decreasing larynx size in adult females and increasing larynx size in adult males?
A) sexual dimorphism was evolving over time in these species
B) intrasexual selection seems to have occurred in these species
C) stabilizing selection was occurring in these species concerning larynx size
D) selection was acting more directly upon genotype than upon phenotype

Accepted Answer

Sexual dimorphism refers to differences in size or appearance between males and females of a species. The trend of increasing larynx size in males and decreasing in females suggests that sexual dimorphism was evolving, likely due to sexual selection pressures.

Question 8

Which of the following reasons best explains why separate populations of a given species are likely to vary genetically from one another?
A) population sizes are likely to differ
B) gene flow increases the similarity among nearby populations
C) environmental and weather conditions vary on a small scale
D) natural selection is the only evolutionary force that improves the match between a population and its environment

Accepted Answer

Environmental and weather conditions vary on a small scale, leading to different selective pressures in different areas, which can cause genetic variation among populations.

Question 9

Three-spined stickleback fish (Gasterosteus aculeatus) show substantial genetic variation in gill-raker length related to differences in their diets. Longer gill rakers appear to function better for capturing open-water prey, while shorter gill rakers function better for capturing shallow-water prey. Which of the following types of selection is most likely to be found in a large lake (open water in the middle and shallow water around the sides) with a high density of these fish?
A) directional selection
B) stabilizing selection
C) disruptive selection
D) sexual selection

Accepted Answer

Disruptive selection is most likely because it favors individuals at both extremes of a trait distribution, in this case, fish with either long or short gill rakers, due to the different feeding advantages in open water versus shallow water.

Question 10

Pigs are vulnerable to infection by bird flu virus and human flu virus, both of which can be present in an individual pig at the same time. When both viruses infect a pig simultaneously, it is possible for genes from bird flu virus and human flu virus to be combined. If the human flu virus contributes a gene for Tamiflu resistance (Tamiflu is an antiviral drug) to the bird flu virus, and if this new virus is introduced to an environment lacking Tamiflu, then which of the following scenarios is most likely to occur?
A) The new virus will maintain its Tamiflu-resistance gene, in case of future exposure to Tamiflu.
B) The Tamiflu-resistance gene will undergo mutations that convert it into a gene that has a useful function in this environment.
C) If the Tamiflu-resistance gene involves a cost, it will experience directional selection leading to reduction in its frequency.
D) If the Tamiflu-resistance gene confers no benefit in the current environment, and has no cost, the virus will increase in frequency.

Accepted Answer

In an environment lacking Tamiflu, if the Tamiflu-resistance gene involves a cost to the virus (e.g., reduced replication efficiency or increased energy expenditure), it will be subject to directional selection that favors viruses without this gene, leading to a reduction in its frequency over time.

Question 11

A researcher has maintained a small population of fruit flies in the laboratory by transferring the flies to a new culture bottle after each generation. After several generations, the viability of the flies decreased greatly. Recognizing that small population size is likely to be linked to decreased viability, which of the following approaches would be the best way to reverse this trend of decreased viability?
A) cross the flies with flies from another lab
B) reduce the number of flies that are transferred at each generation
C) transfer only the largest flies
D) change the temperature at which the flies are reared

Accepted Answer

Crossing the flies with flies from another lab introduces new genetic material, which can increase genetic diversity and potentially reverse the trend of decreased viability due to inbreeding depression in a small, isolated population.

Question 12

Two scientists measured the snout-to-vent (anus) length of Galápagos marine iguanas (lizards) and observed the percent survival of different-sized animals, all of the same age. The graph shows the log snout-vent length (SVL, a measure of overall body size) plotted against the percent survival of these different size classes for males and females.  (Data from M. Wikelski and L. Michael Romero. Body size, performance and fitness in Galapagos marine iguanas. Integrative and Comparative Biology 43:376-386 [2003].)
Currently, the only predators of Galápagos marine iguanas are Galápagos hawks. Although small iguanas can sprint faster than large iguanas, iguana body size is not correlated with risk of hawk predation. If predators (for example, cats) that preferentially catch and eat slower iguanas are introduced to the island, iguana body size is likely to ________ in the absence of other factors; the iguanas would then be under ________ selection.
A) increase; directional
B) increase; disruptive
C) decrease; directional
D) decrease; disruptive

Accepted Answer

The answer of Two scientists measured the snout-to-vent (anus) length...

Question 13

Most Swiss starlings (birds) produce four to five eggs in each clutch. Starlings producing more or less eggs have reduced fitness. Which of the following terms best describes this situation?
A) directional selection
B) stabilizing selection
C) disruptive selection
D) sexual selection

Accepted Answer

Stabilizing selection is the correct term because it describes a type of natural selection in which genetic diversity decreases as the population stabilizes on a particular trait value. In this case, the trait value is the production of four to five eggs, which is favored over other values (more or less), leading to increased fitness for those within this range.

Question 14

Two researchers measured the snout-to-vent (anus) length of Galápagos marine iguanas (lizards) and observed the percent survival of different-sized animals, all of the same age. The graph shows the log snout-vent length (SVL, a measure of overall body size) plotted against the percent survival of these different size classes for males and females.  (Data from M. Wikelski and L. Michael Romero. Body size, performance and fitness in Galapagos marine iguanas. Integrative and Comparative Biology 43:376-386 [2003].)
Based on the data in the figure, what type of selection for body size appears to be occurring in these marine iguanas?
A) directional selection
B) stabilizing selection
C) disruptive selection
D) You cannot determine the type of selection from the above information.

Accepted Answer

The answer of Two researchers measured the snout-to-vent (anus) length...

Question 15

In a very large population, a measurable trait has the distribution pattern shown in the diagram. Assume the trait is genetically determined. If there is no gene flow and the curve shifts to the left or to the right, which of the following processes is most likely occurring?
A) immigration or emigration
B) directional selection
C) disruptive selection
D) genetic drift

Accepted Answer

The answer of  In a very large population, a...

Question 16

Restriction enzymes in bacteria protect the bacteria from successful attack by bacteriophages, whose genomes can be degraded by the restriction enzymes. The bacterial genomes are not vulnerable to these restriction enzymes because bacterial DNA is methylated. This situation selects for bacteriophages whose genomes are also methylated. As new strains of resistant bacteriophages become more prevalent, they in turn select for bacteria whose genomes are not methylated and whose restriction enzymes instead degrade methylated DNA. Which of the following outcomes is most likely to occur over the course of evolutionary time?
A) Methylated DNA should become fixed in the gene pools of bacterial species.
B) Nonmethylated DNA should become fixed in the gene pools of bacteriophages.
C) Methylated DNA should become fixed in the gene pools of bacteriophages.
D) Methylated and nonmethylated strains should be maintained among both bacteria and bacteriophages, with ratios that vary over time.

Accepted Answer

The evolutionary arms race between bacteria and bacteriophages, with changing strategies of DNA methylation and restriction enzyme specificity, suggests that both methylated and nonmethylated strains of bacteria and bacteriophages will coexist. The prevalence of each type will fluctuate over time due to ongoing selective pressures.

Question 17

A biologist doing a long-term study on a wild spider population observes increased variation in silk thickness. Which of the following processes is the most likely to be affecting the spider population?
A) directional selection
B) stabilizing selection
C) disruptive selection
D) genetic drift

Accepted Answer

Disruptive selection is most likely to be affecting the spider population because it favors individuals at both extremes of a trait, in this case, silk thickness, leading to increased variation within the population.

Question 18

Restriction enzymes in bacteria protect the bacteria from successful attack by bacteriophages, whose genomes can be degraded by the restriction enzymes. The bacterial genomes are not vulnerable to these restriction enzymes because bacterial DNA is methylated. This situation selects for bacteriophages whose genomes are also methylated. As new strains of resistant bacteriophages become more prevalent, they in turn select for bacteria whose genomes are not methylated and whose restriction enzymes instead degrade methylated DNA. Which of the following factors is most likely to cause the changes?
A) frequency-dependent selection
B) evolutionary imbalance
C) heterozygote advantage
D) neutral variation

Accepted Answer

Frequency-dependent selection is most likely to cause these changes because the success of the bacteria or bacteriophages depends on the relative frequencies of the different types (methylated vs. non-methylated) in the population. As one type becomes more prevalent, it selects for the opposite type in the other population, leading to a cyclical pattern of adaptation and counter-adaptation.

Question 19

In those parts of equatorial Africa where the malaria parasite is most common, the sickle-cell allele constitutes 20% of the β hemoglobin alleles in the human gene pool.
In the United States, the parasite that causes malaria is not present, but the sickle cell allele is present in many African-Americans whose ancestors were from equatorial Africa. Which of the following processes are most likely acting on the sickle-cell allele in the United States, and in equatorial Africa?
A) stabilizing selection in the United States; disruptive selection in equatorial Africa
B) disruptive selection in the United States; stabilizing selection in equatorial Africa
C) directional selection in the United States; disruptive selection in equatorial Africa
D) directional selection in the United States; stabilizing selection in equatorial Africa

Accepted Answer

In equatorial Africa, the sickle-cell allele provides a selective advantage against malaria, leading to stabilizing selection where both normal and sickle-cell alleles are maintained in the population. In the United States, without the pressure of malaria, the sickle-cell allele may be selected against due to its associated health risks, indicating directional selection towards the normal allele.

Question 20

In some jacana (a bird) species, males take care of the eggs and young, and females compete with each other for territories that contain one to several males. Female jacanas are significantly larger than males. Which of these statements is likely NOT an accurate description of this bird species?
A) Male jacana fitness is primarily limited by the ability to take care of eggs and raise young.
B) Female jacana fitness is limited by the number of males in her territory with which she mates.
C) Variation in reproductive success should be greater in female jacanas than in males.
D) Males and females have equal variation in reproductive success.

Accepted Answer

In species where one sex competes for mates and the other invests more in parental care, the sex that competes for mates (in this case, females) typically shows greater variation in reproductive success than the sex that provides parental care (males). This is because the competitive sex has the potential to mate with multiple partners, leading to a higher variance in the number of offspring.

Quiz 23: Microevolution

The idea of relative fitness is best exemplified in which of the following statements?

Imagine a small herbaceous flowering plant whose conservation status is "endangered." Which of the following possible experiments would best test if a lack of genetic variability was partially responsible for low population numbers?

When a species deviates from a 50:50 sex ratio (male to female) , the members of the minority sex often receive a greater proportion of care and resources from parents than do the offspring of the majority sex. Which of the following processes most likely causes this pattern?

Which of the following statements about evolutionary forces is accurate?

Imagine a human population with an extremely low frequency of sickle cell alleles. Which of the following changes is most likely in the human population 15 generations after introducing a mosquito population that carries the malaria parasite?

Adult male humans generally have deeper voices than do adult female humans. Which of the following processes was most likely occurring given that the fossil records of apes and humans alike show a trend toward decreasing larynx size in adult females and increasing larynx size in adult males?

Which of the following reasons best explains why separate populations of a given species are likely to vary genetically from one another?

Most Swiss starlings (birds) produce four to five eggs in each clutch. Starlings producing more or less eggs have reduced fitness. Which of the following terms best describes this situation?

In a very large population, a measurable trait has the distribution pattern shown in the diagram. Assume the trait is genetically determined. If there is no gene flow and the curve shifts to the left or to the right, which of the following processes is most likely occurring?

A biologist doing a long-term study on a wild spider population observes increased variation in silk thickness. Which of the following processes is the most likely to be affecting the spider population?

In some jacana (a bird) species, males take care of the eggs and young, and females compete with each other for territories that contain one to several males. Female jacanas are significantly larger than males. Which of these statements is likely NOT an accurate description of this bird species?