What is true of the modern evolutionary synthesis?

A) It is about to be declared a scientific law.

B) It is nearing final completion.

C) It has not been able to improve upon Darwin's original ideas about evolution.

D) It remains unable to account for Mendel's findings concerning the genetics of pea plants.

E) It exemplifies the tentative nature of scientific knowledge.

E

A large population of laboratory animals has been allowed to breed randomly for a number of generations. After several generations, 36% of the animals display a recessive trait (aa), the same percentage as at the beginning of the breeding program. The rest of the animals show the dominant phenotype, with heterozygotes indistinguishable from the homozygous dominants.

What is the most reasonable conclusion that can be drawn from the fact that the frequency of the recessive trait (aa) has not changed over time?

A) The population is undergoing genetic drift.

B) The two phenotypes are about equally adaptive under laboratory conditions.

C) The genotype AA is lethal.

D) There has been a high rate of mutation of allele A to allele a.

E) There has been sexual selection favoring allele a.

B

A large population of laboratory animals has been allowed to breed randomly for a number of generations. After several generations, 36% of the animals display a recessive trait (aa), the same percentage as at the beginning of the breeding program. The rest of the animals show the dominant phenotype, with heterozygotes indistinguishable from the homozygous dominants.

What is the estimated frequency of allele a in the gene pool?

A) 0.18

B) 0.40

C) 0.60

D) 0.70

E) 0.80

C

A large population of laboratory animals has been allowed to breed randomly for a number of generations. After several generations, 36% of the animals display a recessive trait (aa), the same percentage as at the beginning of the breeding program. The rest of the animals show the dominant phenotype, with heterozygotes indistinguishable from the homozygous dominants.

What proportion of the population is probably heterozygous (Aa) for this trait?

A) 0.18

B) 0.36

C) 0.48

D) 0.60

E) 0.72

C

All of the following are criteria for maintaining Hardy-Weinberg equilibrium involving two alleles except

A) the frequency of all genotypes must be equal.

B) there should be no natural selection.

C) matings must be random.

D) populations must be large.

E) gene flow from other populations must be zero.

A

In a Hardy-Weinberg population with two alleles, A and a, that are in equilibrium, the frequency of the allele a is 0.7. What is the percentage of the population that is homozygous for this allele?

A) 3

B) 9

C) 30

D) 42

E) 49

E

In a Hardy-Weinberg population with two alleles, A and a, that are in equilibrium, the frequency of allele a is 0.7. What is the percentage of the population that is heterozygous for this allele?

A) 3

B) 9

C) 21

D) 30

E) 42

E

In a Hardy-Weinberg population with two alleles, A and a, that are in equilibrium, the frequency of allele a is 0.2. What is the frequency of individuals with Aa genotype?

A) 0.20

B) 0.32

C) 0.42

D) 0.80

E) Genotype frequency cannot be determined from the information provided.

B

In a population with two alleles, A and a, the frequency of a is 0.50. What would be the frequency of heterozygotes if the population is in Hardy-Weinberg equilibrium?

A) 1.00

B) 0.75

C) 0.50

D) 0.25

E) 0.10

C

Most copies of harmful recessive alleles in a sexual species are carried by individuals that are

A) haploid.

B) polymorphic.

C) homozygous for the allele.

D) heterozygous for the allele.

E) B and C

D

In a population with two alleles, A and a, the frequency of A is 0.2. Organisms that are homozygous for A die before reaching sexual maturity. In five generations, what would be the frequency of individuals with aa genotypes?

A) less than 0.04

B) 0.04

C) 0.32

D) 0.64

E) greater than 0.64

E

You sample a population of butterflies and find that 42% are heterozygous for a particular gene. What would be the frequency of the recessive allele in this population?

A) 0.09

B) 0.30

C) 0.49

D) 0.70

E) Allele frequency cannot be estimated from this information.

E

In a hypothetical population of 1,000 people, tests of blood-type genes show that 160 have the genotype AA, 480 have the genotype AB, and 360 have the genotype BB.

What is the frequency of the A allele?

A) 0.001

B) 0.002

C) 0.100

D) 0.400

E) 0.600

D

In a hypothetical population of 1,000 people, tests of blood-type genes show that 160 have the genotype AA, 480 have the genotype AB, and 360 have the genotype BB.

What is the frequency of the B allele?

A) 0.001

B) 0.002

C) 0.100

D) 0.400

E) 0.600

E

In a hypothetical population of 1,000 people, tests of blood-type genes show that 160 have the genotype AA, 480 have the genotype AB, and 360 have the genotype BB.

What percentage of the population has type O blood?

A) 0

B) 10

C) 24

D) 48

E) 60

A

In a hypothetical population of 1,000 people, tests of blood-type genes show that 160 have the genotype AA, 480 have the genotype AB, and 360 have the genotype BB.

If there are 4,000 children born to this generation, how many would be expected to have AB blood under the conditions of Hardy-Weinberg equilibrium?

A) 100

B) 960

C) 1,920

D) 2,000

E) 2,400

C

In peas, a gene controls flower color such that R = purple and r = white. In an isolated pea patch, there are 36 purple flowers and 64 white flowers. Assuming Hardy-Weinberg equilibrium, what is the value of q for this population?

A) 0.36

B) 0.60

C) 0.64

D) 0.75

E) 0.80

E

Which of the following is not a requirement for maintenance of Hardy-Weinberg equilibrium?

A) an increasing mutation rate

B) random mating

C) large population size

D) no migration

E) no natural selection

A

You are studying three populations of birds. Population 1 has ten birds, of which one is brown (a recessive trait) and nine are red. Population 2 has 100 birds. In that population, ten of the birds are brown. Population 3 has 30 birds, and three of them are brown. Use the following options to answer the questions:

A.Population 1

B.Population 2

C.Population 3

D.They are all the same.

E.It is impossible to tell from the information given.

In which population is the frequency of the allele for brown feathers highest?

D

You are studying three populations of birds. Population 1 has ten birds, of which one is brown (a recessive trait) and nine are red. Population 2 has 100 birds. In that population, ten of the birds are brown. Population 3 has 30 birds, and three of them are brown. Use the following options to answer the questions:

A.Population 1

B.Population 2

C.Population 3

D.They are all the same.

E.It is impossible to tell from the information given.

In which population would it be least likely that an accident would significantly alter the frequency of the brown allele?

B

You are studying three populations of birds. Population 1 has ten birds, of which one is brown (a recessive trait) and nine are red. Population 2 has 100 birds. In that population, ten of the birds are brown. Population 3 has 30 birds, and three of them are brown. Use the following options to answer the questions:

A.Population 1

B.Population 2

C.Population 3

D.They are all the same.

E.It is impossible to tell from the information given.

Which population is most likely to be subject to the bottleneck effect?

A

The probability of a mutation at a particular gene locus is ________, and the probability of a mutation in the genome of a particular individual is ________.

A) high; low

B) low; high

C) low; low

D) high; high

E) moderate; moderate

B

Which factor is the most important in producing the variability that occurs in each generation of humans?

A) mutation

B) sexual recombination

C) genetic drift

D) nonrandom mating

E) natural selection

B

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.

A

Which of the following chromosomal mutations can increase the mass of DNA present in an organism's genome, creating superfluous DNA that may undergo further changes producing entirely new genes?

A) transposition

B) translocation

C) inversion

D) duplication

E) crossing over

D

Genetic recombination is a crucial process in evolution. This statement is supported by the continuous existence of which of the following in evolving populations?

A) sexual reproduction

B) bacterial conjugation

C) exchange of chromosome regions in meiosis (crossing over)

D) A and C only

E) A, B, and C

E

Which is true regarding genetic variation in prokaryotes, where cell reproduction occurs via binary fission?

A) Prokaryotes lack any ability to increase their genetic variation.

B) Prokaryotes are limited to the rare-chance mutation to increase their genetic variation.

C) Only when binary fission occurs by meiosis do prokaryotes have the ability to undergo genetic recombination.

D) Prokaryotic genomes can experience increased genetic variation via both mutation and genetic recombination.

E) Prokaryotic genomes gain genetic variation solely through the action of bacteriophages.

D

In DNA molecules, A-T base pairs are held to each other by two hydrogen bonds, whereas the more stable G-C base pairs are held to each other by three hydrogen bonds. If DNA mutability increases as DNA stability decreases, then which of the five exons of a hypothetical gene should be most highly conserved over evolutionary time (assuming no selection and no transposition occurs)?

A) Exon A

B) Exon B

C) Exon C

D) Exon D

E) Exon E

C

Non-replicative transposons are sections of a DNA molecule that can remove themselves, seal the nicked ends of their former site, and reintegrate themselves somewhere else in the genome. On the other hand, retrotransposons do not remove themselves but, rather, once transcribed as RNA, act as a template for reverse transcriptase. The resulting cDNA can then integrate itself somewhere else in the genome. What is true of retrotransposons that is not generally true of non-replicative transposons?

A) They temporarily exist as RNA intermediates.

B) They can increase the size of an organism's genome.

C) They can cause gene duplication to occur.

D) A, B, and C are true.

E) Only B and C are true.

D

Non-replicative transposons are sections of a DNA molecule that can remove themselves, seal the nicked ends of their former site, and reintegrate themselves somewhere else in the genome. On the other hand, retrotransposons do not remove themselves but, rather, once transcribed as RNA, act as a template for reverse transcriptase. The resulting cDNA can then integrate itself somewhere else in the genome. Unlike other DNA polymerases, reverse transcriptase lacks proofreading capability. In which way(s) should retrotransposons affect the genome that non-replicative transposons do not?

A) They should maintain the amount of DNA in the genome.

B) They should increase the nucleotide variability of the genome.

C) They should increase the number of base-pairs in the genome.

D) Both A and B are true.

E) Both B and C are true.

E

In a large, sexually reproducing population, the frequency of an allele changes from 0.6 to 0.2. From this change, one can most logically assume that, in this environment,

A) the allele is neutral.

B) the allele mutates readily.

C) random processes have changed allelic frequencies.

D) there is no sexual selection.

E) the allele reduces fitness.

E

The following important concepts of population genetics are due to random events or chance except

A) mutation.

B) the bottleneck effect.

C) the founder effect.

D) natural selection.

E) sexual recombination.

D

You are maintaining a small population of fruit flies in the laboratory by transferring the flies to a new culture bottle after each generation. After several generations, you notice that the viability of the flies has decreased greatly. Recognizing that small population size is likely to be linked to decreased viability, the best way to reverse this trend is to

A) cross your flies with flies from another lab.

B) reduce the number of flies that you transfer at each generation.

C) transfer only the largest flies.

D) change the temperature at which you rear the flies.

E) shock the flies with a brief treatment of heat or cold to make them more hardy.

A

If the frequency of a particular allele that is present in a small, isolated population of alpine plants should change due to a landslide that leaves an even smaller remnant of surviving plants, then what has occurred?

A) a bottleneck

B) genetic drift

C) microevolution

D) A and B only

E) A, B, and C

D

Natural selection is most nearly the same as

A) diploidy.

B) gene flow.

C) genetic drift.

D) nonrandom mating.

E) differential reproductive success.

E

Through time, the movement of people on Earth has steadily increased. This has altered the course of human evolution by increasing

A) nonrandom reproduction.

B) geographic isolation.

C) genetic drift.

D) mutations.

E) gene flow.

E

Gene flow is a concept best used to describe an exchange between

A) species.

B) males and females.

C) populations.

D) individuals.

E) chromosomes.

C

In the year 2500, five male space colonists and five female space colonists (all unrelated to each other) settle on an uninhabited Earthlike planet in the Andromeda galaxy. The colonists and their offspring randomly mate for generations. All ten of the original colonists had free earlobes, and two were heterozygous for that trait. The allele for free earlobes is dominant to the allele for attached earlobes.

Which of these is closest to the allele frequency in the founding population?

A) 0.1 a, 0.9 A

B) 0.2 a, 0.8 A

C) 0.5 a, 0.5 A

D) 0.8 a, 0.2 A

E) 0.4 a, 0.6 A

A

In the year 2500, five male space colonists and five female space colonists (all unrelated to each other) settle on an uninhabited Earthlike planet in the Andromeda galaxy. The colonists and their offspring randomly mate for generations. All ten of the original colonists had free earlobes, and two were heterozygous for that trait. The allele for free earlobes is dominant to the allele for attached earlobes.

If one assumes that Hardy-Weinberg equilibrium applies to the population of colonists on this planet, about how many people will have attached earlobes when the planet's population reaches 10,000?

A) 100

B) 400

C) 800

D) 1,000

E) 10,000

A

In the year 2500, five male space colonists and five female space colonists (all unrelated to each other) settle on an uninhabited Earthlike planet in the Andromeda galaxy. The colonists and their offspring randomly mate for generations. All ten of the original colonists had free earlobes, and two were heterozygous for that trait. The allele for free earlobes is dominant to the allele for attached earlobes.

If four of the original colonists died before they produced offspring, the ratios of genotypes could be quite different in the subsequent generations. This is an example of

A) diploidy.

B) gene flow.

C) genetic drift.

D) disruptive selection.

E) stabilizing selection.

C

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) speciation.

A

Which of the following is one important evolutionary feature of the diploid condition?

A) An extra set of genes facilitates the inheritance of characteristics acquired by the previous generation.

B) Recombination can only occur in diploid organisms.

C) DNA in diploid cells is more resistant to mutation than is the DNA of haploid cells.

D) Diploid organisms express less of their genetic variability than haploid organisms.

E) Diploid organisms are more likely to clone successfully than are haploid organisms.

D

The restriction enzymes of 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, this in turn selects for bacteria whose genomes are not methylated and whose restriction enzymes instead degrade methylated DNA.

The outcome of the conflict between bacteria and bacteriophage at any point in time results from

A) frequency-dependent selection.

B) evolutionary imbalance.

C) heterozygote advantage.

D) neutral variation.

E) genetic variation being preserved by diploidy.

A

The restriction enzymes of 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, this in turn selects for bacteria whose genomes are not methylated and whose restriction enzymes instead degrade methylated DNA.

Over the course of evolutionary time, what should occur?

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.

E) Both A and B are correct.

D

The Darwinian fitness of an individual is measured by

A) the number of its offspring that survive to reproduce.

B) the number of supergenes in the genotype.

C) the number of mates it attracts.

D) its physical strength.

E) how long it lives.

A

If a phenotypic polymorphism lacks a genetic component, then

A) the environment cannot affect its abundance.

B) natural selection cannot act upon it to make a population better adapted over the course of generations.

C) it cannot affect an individual's ability to survive.

D) it must exhibit quantitative variation.

E) all of the above.

B

When we say that an individual organism has a greater fitness than another individual, we specifically mean that the organism

A) lives longer than others of its species.

B) competes for resources more successfully than others of its species.

C) mates more frequently than others of its species.

D) utilizes resources more efficiently than other species occupying similar niches.

E) leaves more viable offspring than others of its species.

E

Which of the following statements best summarizes evolution as it is viewed today?

A) It is goal-directed.

B) It represents the result of selection for acquired characteristics.

C) It is synonymous with the process of gene flow.

D) It is the descent of humans from the present-day great apes.

E) It is the differential survival and reproduction of the most fit phenotypes.

E

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

A) nucleotide variability.

B) genetic polymorphism.

C) average heterozygosity.

D) A, B, and C

E) A and B only

D

If neutral variation is truly "neutral," then it should have no effect on

A) nucleotide diversity.

B) average heterozygosity.

C) our ability to measure the rate of evolution.

D) relative fitness.

E) gene diversity.

D

A. random selection

B.directional selection

C.stabilizing selection

D.disruptive selection

E.sexual selection

An African butterfly species exists in two strikingly different color patterns

D

A. random selection

B.directional selection

C.stabilizing selection

D.disruptive selection

E.sexual selection

Brightly colored peacocks mate more frequently than do drab peacocks

E

A. random selection

B.directional selection

C.stabilizing selection

D.disruptive selection

E.sexual selection

Most Swiss starlings produce four to five eggs in each clutch.

C

A. random selection

B.directional selection

C.stabilizing selection

D.disruptive selection

E.sexual selection

Fossil evidence indicates that horses have gradually increased in size over geologic time.

B

A. random selection

B.directional selection

C.stabilizing selection

D.disruptive selection

E.sexual selection

The average birth weight for human babies is about 3 kg.

C

A. random selection

B.directional selection

C.stabilizing selection

D.disruptive selection

E.sexual selection

A certain species of land snail exists as either a cream color or a solid brown color. Intermediate individuals are relatively rare.

D

A. random selection

B.directional selection

C.stabilizing selection

D.disruptive selection

E.sexual selection

Pathogenic bacteria found in many hospitals are antibiotic resistant.

B

Cattle breeders have improved the quality of meat over the years by which process?

A) artificial selection

B) directional selection

C) stabilizing selection

D) A and B

E) A and C

D

The allele that causes phenylketonuria (PKU) is harmful, except when an infant's diet lacks the amino acid, phenylalanine. What maintains the presence of this harmful allele in a population's gene pool?

A) heterozygote advantage

B) stabilizing selection

C) balanced polymorphism

D) diploidy

E) balancing selection

D

Mules are relatively long-lived and hardy organisms that cannot, generally speaking, perform successful meiosis. Which statement about mules is true?

A) They have a relative evolutionary fitness of zero.

B) Their offspring have less genetic variation than the parents.

C) Mutations cannot occur in their genomes.

D) If crossing over happens in mules, then it must be limited to prophase of binary fission.

E) When two mules interbreed, genetic recombination cannot occur by meiotic crossing over, but only by the act of fertilization.

A

Heterozygote advantage should be most closely linked to which of the following?

A) sexual selection

B) stabilizing selection

C) random selection

D) directional selection

E) disruptive selection

B

In equatorial Africa, all of the following factors contribute to keeping the sickle-cell allele at a high frequency in the population, except

A) stabilizing selection.

B) heterozygote advantage.

C) diploidy.

D) balancing selection.

E) frequency-dependent selection.

E

Which statement about variation is most true?

A) All phenotypic variation is the result of genotypic variation.

B) All genetic variation produces phenotypic variation.

C) All nucleotide variability results in neutral variation.

D) All new alleles are the result of nucleotide variability.

E) All geographic variation results from the existence of clines.

D

A balanced polymorphism exists through disruptive selection in seedcracker finches from Cameroon in which small- and large-billed birds specialize in cracking soft and hard seeds, respectively. If long-term climatic change resulted in all seeds becoming hard, what type of selection would then operate on the finch population?

A) disruptive selection

B) directional selection

C) stabilizing selection

D) sexual selection

E) No selection would operate because the population is in Hardy-Weinberg equilibrium.

B

Male satin bowerbirds adorn structures that they build, called "bowers," with parrot feathers, flowers, and other bizarre ornaments in order to attract females. Females inspect the bowers and, if suitably impressed, allow males to mate with them, after which they go off to nest by themselves. The evolution of this behavior is best described as due to

A) survival of the fittest.

B) artificial selection.

C) sexual selection.

D) natural selection.

E) disruptive selection.

C

In many animal species, mature males are much larger than mature females. This size difference can be attributed to

A) male hormones having a more positive effect on body size than female hormones do.

B) the operation of intrasexual selection.

C) females preferentially selecting larger males as mates.

D) A and B only

E) A, B, and C

E

Adult male vervet monkeys have red penises and blue scrotums. Males use their colorful genitalia in dominance displays wherein they compete with each other for access to females. The coloration of the male genitalia is best explained as the result of ________, and specifically of ________.

A) natural selection; stabilizing selection

B) disruptive selection; intrasexual selection

C) sexual selection; intrasexual selection

D) natural selection; intersexual selection

E) sexual selection; disruptive selection

C

Which of the following is most likely to have been produced by sexual selection?

A) a male lion's mane

B) bright colors of female flowers

C) the ability of desert animals to concentrate their urine

D) different sizes of male and female pinecones

E) camouflage coloration in animals

A

When imbalances occur in the sex ratio of sexual species that have two sexes (i.e., other than a 50:50 ratio), 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. This is most clearly an example of

A) sexual selection.

B) disruptive selection.

C) balancing selection.

D) stabilizing selection.

E) frequency-dependent selection.

E

Female wasps, which are protected by the use of a painful stinger, often make their presence conspicuous by rapidly moving their usually long antennae. These wasps are often mimicked by flies with short antennae who give the appearance of rapidly moving long antennae by waving their forelegs in front of their bodies. Which of the following statements concerning this behavior is not consistent with current evolutionary theory?

A) Natural selection cannot fashion perfect organisms.

B) The behavior of the flies may be a compromise if their short antennae are adapted for other uses.

C) Variation in leg-waving behavior may have been present in ancestral populations and available for natural selection, while variation in antennae length may not have.

D) Given enough time, these flies will develop longer antennae and become perfect mimics.

E) Organisms are often locked into historic genetic constraints.

D

The same gene that causes various coat patterns in wild and domesticated cats also causes the cross-eyed condition in these cats, the cross-eyed condition being slightly maladaptive. In a hypothetical environment, the coat pattern that is associated with crossed eyes is highly adaptive, with the result that both the coat pattern and the cross-eyed condition increase in a feline population over time. Which statement is best supported by these observations?

A) Evolution is progressive and tends toward a more perfect population.

B) Phenotype is often the result of compromise.

C) Natural selection reduces the frequency of maladaptive genes in populations over the course of time.

D) Polygenic inheritance is generally maladaptive, and should become less common in future generations.

E) In all environments, coat pattern is a more important survival factor than is eye-muscle tone.

B

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. That the actual forelimbs of these mammals do not seem to be optimally arranged is because

A) natural selection has not had sufficient time to create the optimal design in each case, but will do so given enough time.

B) natural selection operates in ways that are beyond the capability of the human mind to comprehend.

C) in many cases, phenotype is not merely determined by genotype, but by the environment as well.

D) though 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.

E) natural selection is generally limited to modifying structures that were present in previous generations and in previous species.

E

In the hypothetical insect population you examined in the activity "Causes of Microevolution," the genotypic frequency of the green and red bugs changed significantly after a windstorm randomly blew away individuals from the home plant. This change in genotypic frequency can be attributed to

A) gene flow.

B) mutation.

C) genetic drift.

D) natural selection.

E) disruptive selection.

C

What is the result of natural selection?

A) a chance change in the gene pool of a small population

B) the entry of alleles into a population due to immigration

C) a change in the gene pool of a population due to differential reproductive success

D) a change in allelic frequencies due to mutation

E) the loss of alleles from a population due to emigration

C

All the genes in a population are the population's

A) gene pool.

B) fitness.

C) genotype.

D) gene flow.

E) phenotype.

A

In a cell in which 2n = 6, the independent assortment of chromosomes during meiosis can by itself give rise to ________ genetically different gametes.

A) two

B) four

C) six

D) eight

E) ten

D

In sexually reproducing organisms, the events of ________ do not contribute to an increase in genetic variation.

A) prophase I

B) random fertilization

C) metaphase I

D) interphase

E) All of these events do contribute to an increase in genetic variation.

D

In the gene pool of a population with 100 individuals, a fixed allele for a particular gene locus has a frequency of

A) 0.

B) 0.5.

C) 1.

D) 100.

E) cannot be calculated based on this information

C

Researchers examining a particular gene in a fruit fly population discovered that the gene can have either of two slightly different sequences, designated A1 and A2. Further tests showed that 70% of the gametes produced in the population contained the A1 sequence. If the population is at Hardy-Weinberg equilibrium, what proportion of the flies carries both A1 and A2?

A) 0.7

B) 0.49

C) 0.21

D) 0.42

E) 0.09

D

At a locus with a dominant and a recessive allele in Hardy-Weinberg equilibrium, 16% of the individuals are homozygous for the recessive allele. What is the frequency of the dominant allele in the population?

A) 0.84

B) 0.36

C) 0.6

D) 0.4

E) 0.48

C

The average length of jackrabbit ears decreases gradually with increasing latitude. This variation is an example of

A) directional selection.

B) discrete variation.

C) polymorphism.

D) genetic drift.

E) disruptive selection.

A

Which of the following is a polymorphic trait in humans?

A) variation in height

B) variation in intelligence

C) free versus attached earlobes

D) variation in the number of fingers

E) variation in fingerprints

C

Natural selection changes allele frequencies in populations because some ________ survive and reproduce more successfully than others.

A) alleles

B) individual organisms

C) gene pools

D) gene loci

E) species

B

Longer tails of male barn swallows evolve because female barn swallows prefer to mate with the males that have the longest tails. This process is best described as

A) genetic drift that changes the frequencies of the alleles for tail length.

B) natural selection for sexual reproduction that maintains variation in the genes that influence tail length.

C) intersexual selection for traits, such as long tails, that help males attract mates.

D) intrasexual selection for traits, such as long tails, that help males win contests for females.

E) directional selection for traits, such as long tails, that improve males' ability to fly strongly and forage for food over large areas.

C

No two human individuals are alike, except for identical twins. The chief cause of the variation among individuals is

A) new mutations that occurred in the preceding generation.

B) sexual recombination.

C) genetic drift due to the small size of the population.

D) geographic variation within the population.

E) environmental effects.

B

Road construction has isolated a small portion of a beetle population from the main population. After a few generations, this new population exhibits dramatic genetic differences from the old one, most likely because

A) mutations are more common in the new environment.

B) allele frequencies among the stranded beetles differed by chance from those in the parent population's gene pool and subsequent genetic drift caused even more divergence from the original gene pool.

C) the new environment is different from the old, favoring directional selection.

D) gene flow increases in a new environment.

E) members of a small population tend to migrate, removing alleles from the gene pool.

B

Sparrows with average-sized wings survive severe storms better than those with longer or shorter wings, illustrating

A) the bottleneck effect.

B) stabilizing selection.

C) frequency-dependent selection.

D) neutral variation.

E) disruptive selection.

B