Semester 2 AP Bio

When DNA replicates, each strand of the original DNA molecule is used as a template for the synthesis of a second, complementary strand. Which of the following figures most accurately illustrates enzyme-mediated synthesis of new DNA at a replication fork?

(IMAGE)

A particular genetic disorder is associated with a single gene with two alleles. Individuals with two recessive alleles are affected. The prevalence of the disorder is 11 in 6,6006,600. Assuming the population is in Hardy-Weinberg equilibrium, which of the following is closest to the frequency of carriers in the general population?

0.02430

In a sample of 2,400 people, 1,482 were found to have the dominant (taster) phenotype. Assuming that the population is in Hardy-Weinberg equilibrium, approximately how many individuals in the sample are expected to be heterozygous for TAS2R38?

1,133

Stickleback fish are found in both marine and freshwater habitats. The marine fish have no scales but have hardened, armorlike plates along their sides. The plates are thought to protect sticklebacks from certain predators. In the late 1980s, sticklebacks from a marine population colonized Loberg Lake, a freshwater lake in Alaska. Starting in 1990, researchers sampled fish from the lake every four years and recorded the armor-plate phenotypes of the male sticklebacks in each sample. The armor-plate phenotypes were categorized as either complete (plates extending from head to tail), partial (plates extending from head to abdomen), or low (a few plates near the head only). The results are shown in the table below. Which of the following graphs best represents the type of selection most likely operating in the stickleback population of Loberg Lake?

2 humps

Comparison of DNA sequences in Table II suggests that a functional GULO gene in lemurs can have a G, C, or T at position 21 but only a G at position 22. Which of the following pairs of predictions is most helpful in explaining the discrepancy?

A A substitution at position 21 would result inA substitution at position 22 would result inNo change to the protein A premature stop codon or an amino acid with differentbiochemical characteristics

Which of the following statements best supports the claim that organisms share fundamental processes as a result of evolution?

All organisms share a genetic code organized into triplet codons, making it possible for one organism to express a gene from another organism.

The table above shows the types and properties of nitrogencontaining wastes produced by several vertebrates. Which of the following is the best evolutionary explanation of the data?

Ammonia secretion requires a large volume of water and was therefore selected against in terrestrial vertebrates.

Based on morphological characteristics, the phylogenetic tree above has been developed for species I, II, III, and IV. DNA sequencing has recently been completed for a particular gene found in all four species. The sequencing will provide additional information for answering which of the following questions?

Are species III and IV the most closely related?

The functions of the loci of the lac operon shown in the diagram are described in the table below. The diagram above represents a segment of the E. coli chromosome that contains the lacI gene and part of the lac operon, a coordinately regulated set of genes that are required for the metabolism of lactose. The presence of lactose, which causes the repressor to be released from the operator, results in increased transcription of the lac operon. Bacterial cells that contain green fluorescent protein (GFP) will fluoresce under ultraviolet light. Which of the following is the most likely outcome of replacing the lacZ gene in the E. coli lac operon with the gene encoding GFP?

Bacteria growing in the presence of lactose will fluoresce under ultraviolet light.

The functions of the loci of the lac operon shown in the diagram are described in the table below. The diagram above represents a segment of the E. coli chromosome that contains the lacI gene and part of the lac operon, a coordinately regulated set of genes that are required for the metabolism of lactose. The presence of lactose, which causes the repressor to be released from the operator, results in increased transcription of the lac operon. Which of the following is the most likely consequence of a mutation at the operator locus that prevents binding of the repressor protein?

Beta-galactosidase will be produced, even in the absence of lactose.

Which of the following conclusions is supported by the data?

Bonobos are more closely related to humans than to gorillas because bonobos and humans share a more recent common ancestor than bonobos and gorillas do.

Lobe-finned fishes were present in the oceans of the world approximately 400 million years ago. The first tetrapods (vertebrates that had limbs and could move on land) date to about 365 million years ago. One hypothesis states that early tetrapods evolved from lobe-finned fishes. Which of the following is the best plan for testing the hypothesis?

Comparing the arrangements of bones in the fins of lobe-finned fishes and limbs of the earliest tetrapods

Which of the following is most likely to create genetic variation in a population?

DNA polymerase errors during replication

Which of the following scientific questions will best help researchers determine when the nontaster allele arose in the evolutionary history of the selected primates?

Does the nontaster allele exist in any nonhuman primate populations?

A scientist claimed that an E. coli strain had either a mutated trpRtrpR gene or a mutated operator. Which of the following observations most likely supports the claim?

Enzymes required for the synthesis of tryptophan were continuously produced whether tryptophan was absent or present in large quantities.

The three-spined stickleback (Gasterosteus aculeatus) is a small fish found in both marine and freshwater environments. Marine stickleback populations consist mostly of individuals with pronounced pelvic spines, as shown in Figure 1. Individuals in freshwater stickleback populations, on the other hand, typically have reduced pelvic spines, as shown in Figure 2. As represented in Figure 1 and Figure 2, the phenotypic difference between marine and freshwater sticklebacks involves Pitx1, a gene that influences the formation of the jaw, pituitary gland, and pelvic spine. Enhancer sequences upstream of the Pitx1 genetic locus regulate expression of the Pitx1 gene at the appropriate times and in the appropriate tissues during development. Previous studies have found that a mutation in the hindlimb enhancer interferes with the formation of a pronounced pelvic spine. Which of the following best describes how sticklebacks in the same population with identical copies of the Pitx1 gene can still show phenotypic variation in the pelvic spine character?

Expression of the Pitx1 gene is affected by mutations at other genetic loci.

The functions of the loci of the lac operon shown in the diagram are described in the table below. The diagram above represents a segment of the E. coli chromosome that contains the lacI gene and part of the lac operon, a coordinately regulated set of genes that are required for the metabolism of lactose. The presence of lactose, which causes the repressor to be released from the operator, results in increased transcription of the lac operon. Which of the following describes the most likely consequence of a negative feedback pathway involving the lac operon?

Expression of the lac operon diminishes as lactose is depleted.

A researcher is studying two different species. Which of the following sets of observations would best support the claim that the two species have structural similarities as a result of convergent evolution?

GeneticSimilarityFunction ofStructureForm ofStructureLowSameDifferent

A particular genetic disorder results from a single change in the amino acid sequence coded for in a gene. Parts of the sequence in normal and mutated genes are shown below. Normal:TAC CTC GTG GAC TGA GGT CTCTAC CTC GTG GAC TGA GGT CTCMutated:TAC CTC GTG GAC TGA GGT CACTAC CTC GTG GAC TGA GGT CAC Based on the codon chart above, which of the following amino acid changes is most likely found in the mutated protein?

Glu→Val

Experimental evidence shows that the process of glycolysis is present and virtually identical in organisms from all three domains, Archaea, Bacteria, and Eukarya. Which of the following hypotheses could be best supported by this evidence?

Glycolysis is a universal energy-releasing process and therefore suggests a common ancestor for all forms of life.

Toxic substances often have a bitter taste that causes animals who try to eat such substances to spit them out rather than swallow them. Additional data suggest that gorilla populations have a very low frequency of nontasters. Which of the following best describes the likely evolution of the TAS2R38 locus in the gorilla population? A

Gorillas who could taste bitter toxins were more likely to survive and reproduce than nontasters.

Which of the following describes a scenario that would result in the phenotypic change shown in the graph?

House sparrows that lay smaller-than-average clutches of eggs produce fewer viable offspring, while larger-than-average clutches of eggs result in malnourished chicks that have a higher mortality rate.

In a transformation experiment, a sample of E. coli bacteria was mixed with a plasmid containing the gene for resistance to the antibiotic ampicillin (ampr). Plasmid was not added to a second sample. Samples were plated on nutrient agar plates, some of which were supplemented with the antibiotic ampicillin. The results of E. coli growth are summarized below. The shaded area represents extensive growth of bacteria; dots represent individual colonies of bacteria. In a second experiment, the plasmid contained the gene for human insulin as well as the ampr gene. Which of the following plates would have the highest percentage of bacteria that are expected to produce insulin?

IV only

In a transformation experiment, a sample of E. coli bacteria was mixed with a plasmid containing the gene for resistance to the antibiotic ampicillin (ampr). Plasmid was not added to a second sample. Samples were plated on nutrient agar plates, some of which were supplemented with the antibiotic ampicillin. The results of E. coli growth are summarized below. The shaded area represents extensive growth of bacteria; dots represent individual colonies of bacteria. Plates that have only ampicillin-resistant bacteria growing include which of the following?

IV only

The graph above shows the distribution of beak depth in a finch population that had been living on an island under conditions of normal rainfall. During a subsequent drought, the small seeds normally eaten by the finches were less available. Most of the available seeds were large seeds that could be eaten most easily by finches with deep beaks. Which of the following graphs best predicts the distribution of beak depth in the finch population after several years of drought?

Increasing beak width

While there is only one species of Galápagos Island tortoise, there are several subspecies. Larger islands with more wet highlands have lush vegetation near the ground. Tortoises there tend to have high-domed shells and shorter necks, which restrict upward head movement. They also have shorter limbs. They are the heaviest and largest of the subspecies. Smaller, drier islands are inhabited by tortoises with longer necks and limbs and with shells that are elevated above the neck, which allow them to browse taller vegetation. Based on the information given, which of the following is a plausible explanation for the ancestry of the tortoise subspecies?

Individuals with different adaptations in shell shape and leg length best exploited the food resources and left more surviving offspring on each island.

Tubulin genes are evolutionarily derived from the gene that codes for the FtsZ protein.

Mammals on right fish on left

Over several years, bacteria were isolated from members of a human population and tested for antibiotic resistance. The percent of bacterial isolates that were found to be antibiotic resistant is presented in the graph above for each year of the study. Which of the following conclusions is best supported by the information presented in the graph?

Natural selection over multiple generations is favoring antibiotic resistance in the population of bacteria.

Lactose digestion in E. coli begins with its hydrolysis by the enzyme β-galactosidase. The gene encoding β-galactosidase, lacZ, is part of a coordinately regulated operon containing other genes required for lactose utilization. Which of the following figures correctly depicts the interactions at the lac operon when lactose is NOT being utilized? (The legend below defines the shapes of the molecules illustrated in the options.)

No lactose

Which of the following best describes an event during step 2 in the simplified model above?

Noncoding sequences are removed from a newly synthesized RNA molecule.

In a transformation experiment, a sample of E. coli bacteria was mixed with a plasmid containing the gene for resistance to the antibiotic ampicillin (ampr). Plasmid was not added to a second sample. Samples were plated on nutrient agar plates, some of which were supplemented with the antibiotic ampicillin. The results of E. coli growth are summarized below. The shaded area represents extensive growth of bacteria; dots represent individual colonies of bacteria. Which of the following statements best explains why there are fewer colonies on plate IV than on plate III?

Not all E. coli cells are successfully transformed.

Which of the following best describes a characteristic of DNA that makes it useful as hereditary material?

Nucleotide bases in one strand can only be paired with specific bases in the other strand.

Which of the following best explains the changes in the phenotype frequencies of the stickleback population in Loberg Lake?

Predation in the marine environment is different from predation in Loberg Lake.

The hormone prolactin has varying effects in many different animal species. All vertebrates produce prolactin, which is involved in signal transduction pathways. In mammals, prolactin stimulates the production of milk in mammary glands. In fish, prolactin plays an important role in osmoregulation. In birds, prolactin is involved in lipid metabolism. Which of the following best explains the presence of prolactin in various vertebrate species?

Prolactin is a homologous hormone because it has a common origin but different functions in various species.

The three-spined stickleback (Gasterosteus aculeatus) is a small fish found in both marine and freshwater environments. Marine stickleback populations consist mostly of individuals with pronounced pelvic spines, as shown in Figure 1. Individuals in freshwater stickleback populations, on the other hand, typically have reduced pelvic spines, as shown in Figure 2. As represented in Figure 1 and Figure 2, the phenotypic difference between marine and freshwater sticklebacks involves Pitx1, a gene that influences the formation of the jaw, pituitary gland, and pelvic spine. Enhancer sequences upstream of the Pitx1 genetic locus regulate expression of the Pitx1 gene at the appropriate times and in the appropriate tissues during development. Previous studies have found that a mutation in the hindlimb enhancer interferes with the formation of a pronounced pelvic spine. A mutation that affects Pitx1 gene function in all tissue types is most likely to be at which of the following genetic loci?

Promoter

Phenotype is determined, in part, by which genes are expressed. The diagram below illustrates how the product of gene X regulates the expression of other genes. Which of the following statements best explains how protein X regulates gene expression?

Protein X is responsible for activating transcription of some genes but not others.

The three-spined stickleback (Gasterosteus aculeatus) is a small fish found in both marine and freshwater environments. Marine stickleback populations consist mostly of individuals with pronounced pelvic spines, as shown in Figure 1. Individuals in freshwater stickleback populations, on the other hand, typically have reduced pelvic spines, as shown in Figure 2. As represented in Figure 1 and Figure 2, the phenotypic difference between marine and freshwater sticklebacks involves Pitx1, a gene that influences the formation of the jaw, pituitary gland, and pelvic spine. Enhancer sequences upstream of the Pitx1 genetic locus regulate expression of the Pitx1 gene at the appropriate times and in the appropriate tissues during development. Previous studies have found that a mutation in the hindlimb enhancer interferes with the formation of a pronounced pelvic spine. Which of the following describes a possible selective mechanism to explain why freshwater sticklebacks typically have reduced pelvic spines?

Reduced pelvic spines increase the likelihood of escaping predators in freshwater environments.

Which of the following best explains how continuity of genetic information in cells is ensured across generations?

Replication uses a parental strand of DNADNA as a template to create a new strand of DNADNA.

Which of the following samples most likely contains a double-stranded RNARNA virus?

Sample 1

In a scientific study, Plasmodium samples were analyzed in blood drawn from a large number of infected patients before drug treatment and subsequently from the subset of infected patients with drug-resistant Plasmodium. DNA sequences of four different Plasmodium genes thought to be involved in resistance were compared between samples from patients with drug-sensitive Plasmodium and patients with drug-resistant Plasmodium. Which of the following best supports the hypothesis that preexisting mutations confer drug resistance?

Some of the mutations that occur most frequently in samples from patients treated with antimalarial drugs are detectable in Plasmodium samples collected prior to use of antimalarial drugs.

Scientists are interested in determining the evolution of seven lizard species found on different islands of the Canary Island group. They isolated DNADNA from individuals of each species and sequenced the mitochondrial gene that encodes cytochrome b�. The numbers of genetic differences between species are shown in the table below. Based on the data in the table, which of the following lizard species are most closely related?

Species EE and species D

Which of the following phylogenetic trees best illustrates (with the X) the point at which the mutation in the GULO gene most likely occurred during the evolutionary history of these organisms?

Star at chimp

Which of the following describes the most direct effect of a mutation in the DNADNA that encodes a cell's rRNArRNA?

The cell's ability to properly assemble ribosomes and initiate translation will be reduced.

Which of the following best explains how some cells of an individual produce and secrete a specific enzyme, but other cells of the same individual do not?

The cells transcribe and translate different combinations of genes, leading to the production of different sets of proteins.

A scientist adds a chemical to a culture of dividing cells in order to disrupt DNADNA replication. The replicated DNADNA produced by the cells is double-stranded, but sections of it lack covalent bonds between adjacent nucleotides (Figure 1). Figure 1. Replicated DNADNA produced after a chemical is introduced Which of the following claims is best supported by the data?

The chemical inhibits DNADNA ligase.

Which of the following is the most likely effect of the mutation at nucleotide position 7 in the GULO gene of humans?

The deletion of the single nucleotide causes a frame shift, changing the primary structure downstream of the mutation and resulting in a nonfunctional protein.

Which of the following could best explain the change in fur color distribution, as shown in the table above?

The field was primarily composed of light-colored soil and little vegetation, affording gray mice protection from predators.

In a transformation experiment, a sample of E. coli bacteria was mixed with a plasmid containing the gene for resistance to the antibiotic ampicillin (ampr). Plasmid was not added to a second sample. Samples were plated on nutrient agar plates, some of which were supplemented with the antibiotic ampicillin. The results of E. coli growth are summarized below. The shaded area represents extensive growth of bacteria; dots represent individual colonies of bacteria. Which of the following best explains why there is no growth on plate II?

The initial E. coli culture was not ampicillin-resistant.

The three-spined stickleback (Gasterosteus aculeatus) is a small fish found in both marine and freshwater environments. Marine stickleback populations consist mostly of individuals with pronounced pelvic spines, as shown in Figure 1. Individuals in freshwater stickleback populations, on the other hand, typically have reduced pelvic spines, as shown in Figure 2. As represented in Figure 1 and Figure 2, the phenotypic difference between marine and freshwater sticklebacks involves Pitx1, a gene that influences the formation of the jaw, pituitary gland, and pelvic spine. Enhancer sequences upstream of the Pitx1 genetic locus regulate expression of the Pitx1 gene at the appropriate times and in the appropriate tissues during development. Previous studies have found that a mutation in the hindlimb enhancer interferes with the formation of a pronounced pelvic spine. In sticklebacks, which of the following is most likely to occur if the jaw enhancer is disabled instead of the hindlimb enhancer?

The jaw does not develop normally, but a pronounced pelvic spine does develop because the Pitx1 gene is expressed in the developing pelvis but not in the developing jaw.

The functions of the loci of the lac operon shown in the diagram are described in the table below. The diagram above represents a segment of the E. coli chromosome that contains the lacI gene and part of the lac operon, a coordinately regulated set of genes that are required for the metabolism of lactose. The presence of lactose, which causes the repressor to be released from the operator, results in increased transcription of the lac operon. Which of the following best explains the contribution of the lac operon to the metabolic efficiency of a bacterial cell?

The lacZ gene is highly expressed only when lactose is available.

Which of the following best explains why ligase is required for DNADNA replication?

The lagging strand cannot be replicated continuously, and ligase is needed to join the fragments.

Beta thalassemia is a disorder caused by mutations in the HBBHBB gene. Examination of the HBBHBB protein in an individual with beta thalassemia shows that the protein is missing many amino acids at its carboxyl terminus. Which of the following is the most likely explanation for how a mutation in the DNADNA could result in the loss of the carboxyl terminus of the HBBHBB protein?

The mutation changes a codon in the coding region of the HBBHBB transcript to a stop codon such that translation terminates earlier than it should.

Sea otters are native to the western coast of North America. Between 1750 and 1850, hunting had reduced the population from hundreds of thousands to only one thousand individuals. In the early 1900s, a small population of sea otters was discovered in Elkhorn Slough, an estuary in central California near a large human population center. The otters were then protected by the international fur seal treaty, which banned sea otter hunting. The sea otter population has rebounded to nearly three thousand individuals today. Otters live in kelp forests and eelgrass beds and feed on crabs and shellfish (Figure 1). Most herbivores in the habitat eat algae that grows on the eelgrass and not the eelgrass itself. If there is too much algae, the eelgrass does not receive enough light for photosynthesis. As the otter population has increased, the eelgrass habitat has increased. Figure 1. Partial food chain in eelgrass habitats Recently, however, scientists have noticed the presence of two nonnative, predatory invertebrate species that may be colonizing the Elkhorn Slough, which would have been too cold for them three decades ago. Scientists have also observed that otters in the area are experiencing increased mortality because of an increase in harmful algal blooms, which occur as a result of nutrient pollution. The harmful algae are ingested by shellfish, which the otters eat. Which of the following best describes what happened to the otter population between 1750 and 1850 ? A

The population lost genetic diversity as a result of a bottleneck effect.

The regulatory sequences of the operon controlling arabinose metabolism (ara operon) were studied to determine whether bacteria can respond to changes in nutrient availability. It is predicted that if those regulatory sequences are functioning properly, the bacteria will produce the enzymes involved in arabinose metabolism (structural genes B, A, and D) in the presence of arabinose. If a gene that encodes a green fluorescent protein (GFP) is substituted for the structural genes of the operon, activation of the regulatory sequences can be assayed by GFP expression. A culture of E. coli cells underwent a transformation procedure with a plasmid containing the regulatory sequences of the ara operon directly upstream of the gene encoding the GFP. The plasmid also confers ampicillin resistance to bacteria. Samples were then plated on different types of culture media. (Note: The GFP fluoresces only under UV light, not under white light.) The table below shows the results. Which of the following can best be used to justify why the GFP is expressed by E. coli cells after transformation with the plasmid?

The presence of arabinose in the nutrient agar activated the expression of the genes located downstream of the ara operon regulatory sequences.

Which of the following best explains how the expression of a eukaryotic gene encoding a protein will differ if the gene is expressed in a prokaryotic cell instead of in a eukaryotic cell?

The protein will be made but will not function, because prokaryotes cannot remove introns.

The following the DNA sequence is a small part of the coding (nontemplate) strand from the open reading frame of β-hemoglobin gene. Given the codon chart listed below, what would be the effect of a mutation that deletes the G at the beginning of the DNA sequence? 5'- GTT TGT CTG TGG TAC CAC GTG GAC TGA - 3' A The mutation precedes the gene, so no changes would occur. B Lysine (lys) would replace glutamine (gln), but there would be no other changes. C The first amino acid would be missing, but there would be no other change to the protein. D The reading frame of the sequence would shift, causing a change in the amino acid sequence after that point. Related Content & Skills Topic6.4

The reading frame of the sequence would shift, causing a change in the amino acid sequence after that point.

Sugar gliders and Northern flying squirrels are mammals that have many morphological similarities despite being genetically different. Both are nocturnal and have large eyes to help them see in the dark. Both live in trees and have flaps of skin connecting their front and back legs, and when their front and back legs are extended, the flaps allow the animals to glide from one tree branch to another. Sugar gliders are native to Australia, and Northern flying squirrels are native to North America. Which of the following best explains the morphological similarities between these two species?

The similarities between the species evolved independently as a result of similar selective pressures in each species' environment.

Which of the following pieces of evidence best supports the hypothesis that birds and crocodilians (crocodiles and alligators) are more closely related to each other than they are to other organisms?

The skulls of birds and crocodilians have an opening that is absent in the skulls of other reptiles.

Which of the following best describes a characteristic of the process shown in Figure 1 that is unique to prokaryotes?

The translation of the mRNAmRNA is occurring while the mRNAmRNA is still being transcribed.

Goats and sheep belong to the same family but different genera. While they often live together in the same pastures, the hybrid offspring that are occasionally produced between the two species rarely survive. When such a hybrid does survive, it is usually sterile. Which of the following best explains the mechanism that maintains reproductive isolation between goats and sheep?

The two species have a different number of chromosomes, resulting in a postzygotic barrier.

Both species of garter snakes prey on the California newt, Taricha torosa, a small amphibian that produces a potent neurotoxin (TTX) in its skin. However, neither species of garter snake is affected by TTX. The resistance to TTX is associated with mutations in the SCN4A gene. Which of the following best supports a claim that TTX resistance arose independently in T. atratus and T. sirtalis ?

The two species of snakes have different genetic mutations in the SCN4A gene.

Which of the following observations would provide the strongest evidence that two plants belong to different biological species?

They produce viable but sterile offspring.

The FtsZ protein is present in prokaryotes and in chloroplasts. The protein is structurally and functionally similar to tubulin proteins of eukaryotic cells. Which of the following is a likely conclusion to draw from this information?

Tubulin genes are evolutionarily derived from the gene that codes for the FtsZ protein.

In a transformation experiment, a sample of E. coli bacteria was mixed with a plasmid containing the gene for resistance to the antibiotic ampicillin (ampr). Plasmid was not added to a second sample. Samples were plated on nutrient agar plates, some of which were supplemented with the antibiotic ampicillin. The results of E. coli growth are summarized below. The shaded area represents extensive growth of bacteria; dots represent individual colonies of bacteria. Plates I and III were included in the experimental design in order to

demonstrate that the E. coli cultures were viable

In prokaryotes, the genes of the trptrp operon encode enzymes used in the synthesis of tryptophan. The genes of the trptrp operon are actively expressed (Figure 1A) unless abundant tryptophan is present in the environment. When tryptophan is abundant, some tryptophan binds to the trptrp repressor protein, which in turn causes the repressor to bind to the operator and block transcription of the genes (Figure 1B). The repressor protein is encoded by the trpRtrpR gene which is not a part of the trptrp operon. Figure 1A. When tryptophan is absent, the trptrp operon is active. Figure 1B. When tryptophan is abundant, the trptrp operon is inactivated by the binding of the repressor protein to the operator. Which of the following best supports a claim that an E. coli strain has a mutation in gene EE that results in the production of a nonfunctional enzyme?

mRNA is continuously transcribed from the operon, but the amount of tryptophan produced from the cells of this strain remains low.

Which of the following questions will most likely allow the scientist to design an experiment to determine whether unregulated tryptophan synthesis in a strain of E. coli is caused by a mutation in the trpRtrpR gene or in the operator of the trptrp operon?

s normal regulation of tryptophan synthesis restored when a gene encoding a normal repressor protein is introduced into and expressed by this strain of E. coli?

Transcription of the structural genes in an inducible operon

starts when the pathway's substrate is present