In cats, black fur color is caused by an X-linked allele; the other allele at this locus causes orange color. The heterozygote is tortoiseshell. What kinds of offspring would you expect from the cross of a black female and an orange male?
A) tortoiseshell females; tortoiseshell males
B) black females; orange males
C) orange females; orange males
D) tortoiseshell females; black males
E) orange females; black males

D

Red-green color blindness is a sex-linked recessive trait in humans. Two people with normal color vision have a color-blind son. What are the genotypes of the parents?
A) XcXc and XcY
B) XcXc and XCY
C) XCXC and XcY
D) XCXC and XCY
E) XCXc and XCY

E

Cinnabar eyes is a sex-linked recessive characteristic in fruit flies. If a female having cinnabar eyes is crossed with a wild-type male, what percentage of the F₁ males will have cinnabar eyes?
A) 0%
B) 25%
C) 50%
D) 75%
E) 100%

C

Normally, only female cats have the tortoiseshell phenotype because _____.

A) a male inherits only one allele of the X-linked gene controlling hair color

B) the Y chromosome has a gene blocking orange coloration

C) only males can have Barr bodies

D) multiple crossovers on the Y chromosome prevent orange pigment production

A

In birds, sex is determined by a ZW chromosome scheme. Males are ZZ and females are ZW. A recessive lethal allele that causes death of the embryo is sometimes present on the Z chromosome in pigeons. What would be the sex ratio in the offspring of a cross between a male that is heterozygous for the lethal allele and a normal female?
A) 2:1 male to female
B) 1:2 male to female
C) 1:1 male to female
D) 4:3 male to female
E) 3:1 male to female

A

Duchenne muscular dystrophy is a serious condition caused by a recessive allele of a gene on the human X chromosome. The patients have muscles that weaken over time because they have absent or decreased dystrophin, a muscle protein. They rarely live past their twenties. How likely is it for a woman to have this condition?

A) Women can never have this condition.

B) One-fourth of the daughters of an affected man would have this condition.

C) One-half of the daughters of an affected father and a carrier mother could have this condition.

D) Only if a woman is XXX could she have this condition.

E) One-half of the daughters of an affected father and a

C

A man who is an achondroplastic dwarf with normal vision marries a color-blind woman of normal height. The man's father was six feet tall, and both the woman's parents were of average height. Achondroplastic dwarfism is autosomal dominant, and red-green color blindness is X-linked recessive. How many of their daughters might be expected to be color-blind dwarfs?

A) none

B) half

C) one out of four

D) three out of four

A

A recessive allele on the X chromosome is responsible for red-green color blindness in humans. A woman with normal vision whose father is color blind marries a color-blind male. What is the probability that this couple's first son will be color blind?

A) 1/4

B) 1/2

C) 2/3

D) 3/4

B

In a Drosophila experiment, a cross was made between homozygous wild-type females and yellow-bodied males. All of the resulting F1s were phenotypically wild type. However, adult flies of the F2 generation (resulting from matings of the F1s) had the characteristics shown in the figure above. Consider the following questions:

(a) Is the mutant allele for yellow body recessive or dominant?

(b) Is the yellow locus autosomal (not X-linked) or X-linked?

A) (a) recessive; (b) X-linked

B) (a) recessive; (b) not X-linked

C) (a) dominant; (b) X-linked

D) (a) dominant; (b) not X-linked

A

What is the definition of one map unit?

A) the physical distance between two linked genes

B) a 1% frequency of recombination between two genes

C) 1 nanometer of distance between two genes

D) the recombination frequency between two genes assorting independently

B

The greatest distance among the three genes is between a and c. What does this mean?

A) Gene c is between a and

B) Genes are in the order: a—b—c.

C) Gene a is not recombining with

D) Gene a is between b and

B

If cell X enters meiosis, and nondisjunction of one chromosome occurs in one of its daughter cells during meiosis II, what will be the result at the completion of meiosis?

A) All the gametes descended from cell X will be diploid.

B) Half of the gametes descended from cell X will be n + 1, and half will be n - 1.

C) 1/4 of the gametes descended from cell X will be n + 1, 1/4 will be n - 1, and 1/2 will be n.

D) Two of the four gametes descended from cell X will be haploid, and two will be diploid.

C

Of the following human aneuploidies, which is the one that generally has the most severe impact on the health of the individual?

A) 47, trisomy 21

B) 47, XXY

C) 47, XXX

D) 45, X

A

A couple has a child with Down syndrome. The mother is 39 years old at the time of delivery. Which of the following is the most probable cause of the child's condition?
A) The woman inherited this tendency from her parents.
B) One member of the couple carried a translocation.
C) One member of the couple underwent nondisjunction in somatic cell production.
D) One member of the couple underwent nondisjunction in gamete production.
E) The mother had a chromosomal duplication.

D

Correns described that the inheritance of variegated color on the leaves of certain plants was determined by the maternal parent only. What phenomenon does this describe?
A) mitochondrial inheritance
B) chloroplast inheritance
C) genomic imprinting
D) infectious inheritance
E) sex-linkage

B

Mitochondrial DNA is primarily involved in coding for proteins needed for electron transport. Therefore, in which body systems would you expect most mitochondrial gene mutations to be exhibited?
A) the immune system and the blood
B) the excretory and respiratory systems
C) the skin and senses
D) the nervous and muscular systems
E) the circulation system

D

The pedigree in Figure 15.3 shows the transmission of a trait in a particular family. Based on this pattern of transmission, the trait is most likely
A) mitochondrial.
B) autosomal recessive.
C) sex-linked dominant.
D) sex-linked recessive.
E) autosomal dominant.

A

During meiosis, a defect occurs in a cell that results in the failure of microtubules, spindle fibers, to bind at the kinetochores, a protein structure on chromatids where the spindle fibers attach during cell division to pull sister chromatids apart. Which of the following is the most likely result of such a defect?

A) New microtubules with more effective binding capabilities to kinetochores will be synthesized to compensate for the defect.

B) Excessive cell divisions will occur resulting in cancerous tumors and an increase in the chromosome numbers known as polyploidy.

C) The defect will be bypassed in order to and ensure normal chromosome distribution in the new cells.

D) The resulting cells will not receive the correct number of chromosomes in the gametes, a condition known as aneuploidy.

D

Inheritance patterns cannot always be explained by Mendel’s models of inheritance. If a pair of homologous chromosomes fails to separate during meiosis I, select the choice

that shows the chromosome number of the four resulting gametes with respect to the normal haploid number (n)?

A) n+1; n+1; n-1; n-1

B) n+1; n-1; n; n

C) n+1; n-1; n-1; n-1

D) n+1; n+1; n; n

A

In his transformation experiments, what did Griffith observe?
A) Mutant mice were resistant to bacterial infections.
B) Mixing a heat-killed pathogenic strain of bacteria with a living nonpathogenic strain can convert some of the living cells into the pathogenic form.
C) Mixing a heat-killed nonpathogenic strain of bacteria with a living pathogenic strain makes the pathogenic strain nonpathogenic.
D) Infecting mice with nonpathogenic strains of bacteria makes them resistant to pathogenic strains.
E) Mice infected with a pathogenic strain of bacteria can spread the infection to other mice.

B

Which of the following investigators was/were responsible for the following discovery?
In DNA from any species, the amount of adenine equals the amount of thymine, and the amount of guanine equals the amount of cytosine.
A) Frederick Griffith
B) Alfred Hershey and Martha Chase
C) Oswald Avery, Maclyn McCarty, and Colin MacLeod
D) Erwin Chargaff

D

For a science fair project, two students decided to repeat the Hershey and Chase experiment, with modifications. They decided to label the nitrogen of the DNA, rather than the phosphate. They reasoned that each nucleotide has only one phosphate and two to five nitrogens. Thus, labeling the nitrogens would provide a stronger signal than labeling the phosphates. Why won't this experiment work?

A) There is no radioactive isotope of nitrogen.
B) Radioactive nitrogen has a half-life of 100,000 years, and the material would be too dangerous for too long.
C) Avery et al. have already concluded that this experiment showed inconclusive results.
D) Although there are more nitrogens in a nucleotide, labeled phosphates actually have 16 extra neutrons; therefore, they are more radioactive.
E) Amino acids (and thus proteins) also have nitrogen atoms; thus, the radioactivity would not distinguish between DNA and proteins.

E

In the polymerization of DNA, a phosphodiester bond is formed between a phosphate group of the nucleotide being added and _____ of the last nucleotide in the polymer.

1. A) the 5' phosphate
2. B) C6
3. C) the 3' OH
4. D) a nitrogen from the nitrogen-containing bas

C

At a specific area of a chromosome, the sequence of nucleotides below is present where the chain opens to form a replication fork:

3' C C T A G G C T G C A A T C C 5'

An RNA primer is formed starting at the underlined T (T) of the template. Which of the following represents the primer sequence?

1. A) 5' G C C T A G G 3'
2. B) 5' A C G T T A G G 3'
3. C) 5' A C G U U A G G 3'
4. D) 5' G C C U A G G 3

C

The difference between ATP and the nucleoside triphosphates used during DNA synthesis is that _____.

A) the nucleoside triphosphates have the sugar deoxyribose; ATP has the sugar ribose

B) the nucleoside triphosphates have two phosphate groups; ATP has three phosphate groups

C) ATP contains three high-energy bonds; the nucleoside triphosphates have two

D) ATP is found only in human cells; the nucleoside triphosphates are found in all animal and plant cells

A

Which of the following help(s) to hold the DNA strands apart while they are being replicated?

A) primase

B) ligase

C) DNA polymerase

D) single-strand DNA binding proteins

D

In the late 1950s, Meselson and Stahl grew bacteria in a medium containing "heavy" nitrogen (15N) and then transferred them to a medium containing 14N. Which of the results in the figure above would be expected after one round of DNA replication in the presence of 14N?

1. A) A
2. B) B
3. C) C
4. D) D

D

A space probe returns with a culture of a microorganism found on a distant planet. Analysis shows that it is a carbon-based life-form that has DNA. You grow the cells in 15N medium for several generations and then transfer them to 14N medium. Which pattern in the figure above would you expect if the DNA was replicated in a conservative manner?

1. A) A
2. B) B
3. C) C
4. D) D

B

After the first replication was observed in their experiments testing the nature of DNA replication, Meselson and Stahl could be confident of which of the following conclusions?

A) Replication is semi-conservative.

B) Replication is not dispersive.

C) Replication is not conservative.

D) Replication is neither dispersive nor conservative.

C

Semiconservative replication involves a template. What is the template?

A) single-stranded binding proteins

B) DNA polymerase

C) one strand of the DNA molecule

D) an RNA molecule

C

What is the difference between the leading strand and the lagging strand in DNA replication?

1. A) The leading strand is synthesized in the 3'→5' direction in a discontinuous fashion, while the lagging strand is synthesized in the 5'→3' direction in a continuous fashion.
2. B) The leading strand is synthesized continuously in the5'→3' direction, while the lagging strand is synthesized discontinuously in the 5' → 3'
3. C) The leading strand requires an RNA primer, whereas the lagging strand does not.
4. D) There are different DNA polymerases involved in elongation of the leading strand and the lagging strand

B

What is a major difference between eukaryotic DNA replication and prokaryotic DNA replication?

1. A) Prokaryotic replication does not require a primer.
2. B) Prokaryotic chromosomes have a single origin of replication, while eukaryotic chromosomes have multiple origins of replication.
3. C) DNA replication in prokaryotic cells is conservative. DNA replication in eukaryotic cells is semi-conservative.
4. D) DNA polymerases of prokaryotes can add nucleotides to both 3’and 5’ends of DNA strands, while those of eukaryotes function only in the 5’ → 3’

B

Telomere shortening puts a limit on the number of times a cell can divide. Research has shown that telomerase can extend the life span of cultured human cells. How might adding telomerase affect cellular aging?

A) Telomerase will speed up the rate of cell proliferation.

B) Telomerase eliminates telomere shortening and retards aging.

C) Telomerase shortens telomeres, which delays cellular aging.

D) Telomerase would have no effect on cellular aging.

B

Which of the following statements describes a eukaryotic chromosome?

A) a single strand of DNA

B) a series of nucleosomes wrapped around two DNA molecules

C) a chromosome with different numbers of genes in different cell types of an organism

D) a single linear molecule of double-stranded DNA plus proteins

D

If a cell were unable to produce histone proteins, which of the following would be a likely effect?

A) There would be an increase in the amount of "satellite" DNA produced during centrifugation.

B) The cell's DNA couldn't be packed into its nucleus.

C) Spindle fibers would not form during prophase.

D) Amplification of other genes would compensate for the lack of histones.

B

Which of the following represents the order of increasingly higher levels of organization of chromatin?

A) nucleosome, 30-nm chromatin fiber, looped domain

B) looped domain, 30-nm chromatin fiber, nucleosome

C) nucleosome, looped domain, 30-nm chromatin fiber

D) 30-nm chromatin fiber, nucleosome, looped domain

A

In E. coli replication the enzyme primase is used to attach a 5 to 10 base ribonucleotide strand complementary to the parental DNA strand. The RNA strand serves as a starting point for the DNA

polymerase that replicates the DNA. If a mutation occurred in the primase gene, which of the following would you expect?

A) Replication would only occur on the leading strand.

B) Replication would only occur on the lagging strand.

C) Replication would not occur on either the leading or lagging strand.

D) Replication would not be affected as the enzyme primase in involved with RNA synthesis.

C

Garrod hypothesized that "inborn errors of metabolism" such as alkaptonuria occur because
A) metabolic enzymes require vitamin cofactors, and affected individuals have significant nutritional deficiencies.
B) enzymes are made of DNA, and affected individuals lack DNA polymerase.
C) many metabolic enzymes use DNA as a cofactor, and affected individuals have mutations that prevent their enzymes from interacting efficiently with DNA.
D) certain metabolic reactions are carried out by ribozymes, and affected individuals lack key splicing factors.
E) genes dictate the production of specific enzymes, and affected individuals have genetic defects that cause them to lack certain enzymes.

A

he genetic code is essentially the same for all organisms. From this, one can logically assume which of the following?
A) A gene from an organism can theoretically be expressed by any other organism.
B) All organisms have experienced convergent evolution.
C) DNA was the first genetic material.
D) The same codons in different organisms translate into the different amino acids.

A

A possible sequence of nucleotides in the template strand of DNA that would code for the polypeptide sequence phe-leu-ile-val would be
A) 5' TTG-CTA-CAG-TAG 3'.
B) 3' AAC-GAC-GUC-AUA 5'.
C) 5' AUG-CTG-CAG-TAT 3'.
D) 3' AAA-AAT-ATA-ACA 5'.
E) 3' AAA-GAA-TAA-CAA 5'.

E

What amino acid sequence will be generated, based on the following mRNA codon sequence?
5' AUG-UCU-UCG-UUA-UCC-UUG 3'
A) met-arg-glu-arg-glu-arg
B) met-glu-arg-arg-glu-leu
C) met-ser-leu-ser-leu-ser
D) met-ser-ser-leu-ser-leu

D

According to the central dogma, what molecule should go in the blank?

DNA → _____ → Proteins

A) mtDNA

B) rRNA

C) mRNA

D) tRNA

C

Which of the following statements best describes the termination of transcription in prokaryotes?

A) RNA polymerase transcribes through the polyadenylation signal, causing proteins to associate with the transcript and cut it free from the polymerase.

B) RNA polymerase transcribes through the terminator sequence, causing the polymerase to separate from the DNA and release the transcript.

C) Once transcription has initiated, RNA polymerase transcribes until it reaches the end of the chromosome.

D) RNA polymerase transcribes through a stop codon, causing the polymerase to stop advancing through the gene and release the mRNA.

B

Alternative RNA splicing _____.

A) is a mechanism for increasing the rate of translation

B) can allow the production of proteins of different sizes and functions from a single mRNA

C) can allow the production of similar proteins from different RNAs

D) increases the rate of transcription

B

In an experimental situation, a student researcher inserts an mRNA molecule into a eukaryotic cell after she has removed its cap and poly-A tail. Which of the following would you expect her to find?

A) The mRNA is quickly converted into a ribosomal subunit.

B) The cell adds a new poly-A tail to the mRNA.

C) The mRNA attaches to a ribosome and is translated, but more slowly.

D) The molecule is digested by enzymes because it is not protected at the end.

D

Which components of the previous molecule will also be found in mRNA in the cytosol?

A) UTR I1 I2 I3 UTR

B) E1 E2 E3 E4

C) UTR E1 E2 E3 E4 UTR

D) E1 I1 E2 I2 E3 I3 E4

C

A particular triplet of bases in the coding sequence of DNA is AAA. The anticodon on the tRNA that binds the mRNA codon is _____.

A) TTT

B) UUA

C) UUU

D) AAA

D

Accuracy in the translation of mRNA into the primary structure of a polypeptide depends on specificity in the _____.

A) binding of ribosomes to mRNA

B) binding of the anticodon to small subunit of the ribosome

C) attachment of amino acids to rRNAs

D) binding of the anticodon to the codon and the attachment of amino acids to tRNAs

D

Which one of the following statements about RNA processing is true?

A) Exons are cut out before mRNA leaves the nucleus.

B) Ribozymes may function in RNA splicing.

C) RNA splicing can be catalyzed by tRNA.

D) A primary transcript is often much shorter than the final RNA molecule that leaves the nucleus.

B

A primary transcript in the nucleus of a eukaryotic cell is _____ the functional mRNA, while a primary transcript in a prokaryotic cell is _____ the functional mRNA.

A) the same size as; smaller than

B) larger than; the same size as

C) larger than; smaller than

D) the same size as; larger than

B

In the structural organization of many eukaryotic genes, individual exons may be related to which of the following?

A) the sequence of the intron that immediately precedes each exon

B) the number of polypeptides making up the functional protein

C) the various domains of the polypeptide product

D) the number of start sites for transcription

C

In eukaryotes there are several different types of RNA polymerase. Which type is involved in transcription of mRNA for a globin protein?

A) RNA polymerase I

B) RNA polymerase II

C) RNA polymerase III

D) primase

B

Transcription in eukaryotes requires which of the following in addition to RNA polymerase?

A) start and stop codons

B) ribosomes and tRNA

C) several transcription factors

D) aminoacyl-tRNA synthetase

C

Which of the following best describes the significance of the TATA box in eukaryotic promoters?

A) It is the recognition site for a specific transcription factor.

B) It sets the reading frame of the mRNA.

C) It is the recognition site for ribosomal binding.

D) Its significance has not yet been determined.

A

Which of the following does not occur in prokaryotic gene expression, but does occur in eukaryotic gene expression?

A) mRNA, tRNA, and rRNA are transcribed.

B) RNA polymerase binds to the promoter.

C) A cap is added to the end of the mRNA.

D) RNA polymerase requires a primer to elongate the molecule.

C

A ribozyme is _____.

A) a catalyst that uses RNA as a substrate

B) an RNA with catalytic activity

C) an enzyme that catalyzes the association between the large and small ribosomal subunits

D) an enzyme that synthesizes RNA as part of the transcription process

B

In eukaryotes there are several different types of RNA polymerase. Which type is involved in transcription of mRNA for a globin protein?

A) RNA polymerase I

B) RNA polymerase II

C) RNA polymerase III

D) primase

B

Transcription in eukaryotes requires which of the following in addition to RNA polymerase?

A) start and stop codons

B) ribosomes and tRNA

C) several transcription factors

D) aminoacyl-tRNA synthetase

C

Codons are three-base sequences that specify the addition of a single amino acid. How do eukaryotic codons and prokaryotic codons compare?

A) Prokaryotic codons usually contain different bases than those of eukaryotes.

B) Prokaryotic codons usually specify different amino acids than those of eukaryotes.

C) The translation of codons is mediated by tRNAs in eukaryotes, but translation requires no intermediate molecules such as tRNAs in prokaryotes.

D) Codons are a nearly universal language among all organisms.

C

Which of the following occurs in prokaryotes but not in eukaryotes?

A) post-transcriptional splicing

B) concurrent transcription and translation

C) translation in the absence of a ribosome

D) gene regulation

B

Refer to the figure above. What would the anticodon be for a tRNA that transports phenylalanine to a ribosome?

A) UUU

B) AAA

C) TTT

D) CCC

B

Which of the following contradicts the one-gene, one-enzyme hypothesis?

A) A mutation in a single gene can result in a defective protein.

B) Alkaptonuria results when individuals lack a single enzyme involved in the catalysis of homogentisic acid.

C) Sickle-cell anemia results in defective hemoglobin.

D) A single antibody gene can code for different related proteins, depending on the splicing that takes place post-transcriptionally.

D

Which of the following is directly related to a single amino acid?

A) the base sequence of the tRNA

B) the amino acetyl tRNA synthase

C) the three-base sequence of mRNA

D) the complementarity of DNA and RNA

C

In the process of transcription, _____.

A) DNA is replicated

B) RNA is synthesized

C) proteins are synthesized

D) mRNA attaches to ribosomes

B

Codons are part of the molecular structure of _____.

A) a protein

B) mRNA

C) tRNA

D) rRNA

B

What does it mean when we say the genetic code is redundant?

A) A single codon can specify the addition of more than one amino acid.

B) The genetic code is different for different domains of organisms.

C) The genetic code is universal (the same for all organisms).

D) More than one codon can specify the addition of the same amino acid.

D

Once researchers identified DNA as the unit of inheritance, they asked how information was transferred from the DNA in the nucleus to the site of protein synthesis in the cytoplasm. What is the mechanism of information transfer in eukarotes?

A) DNA from a single gene is replicated and transferred to the cytoplasm, where it serves as a template for protein synthesis.

B) Messenger RNA is transcribed from a single gene and transfers information from the DNA in the nucleus to the cytoplasm, where protein synthesis takes place.

C) Proteins transfer information from the nucleus to the ribosome, where protein synthesis takes place.

D) Transfer RNA takes information from DNA directly to a ribosome, where protein synthesis takes place.

B

The figure above shows a simple metabolic pathway. According to Beadle and Tatum's hypothesis, how many genes are necessary for this pathway?

A) 1

B) 2

C) 3

D) It cannot be determined from the pathway.

B

Refer to the metabolic pathway illustrated above. If A, B, and C are all required for growth, a strain that is mutant for the gene-encoding enzyme A would be able to grow on medium supplemented with _____.

A) nutrient A only

B) nutrient B only

C) nutrient C only

D) nutrients A and C

B

Refer to the metabolic pathway illustrated above. If A, B, and C are all required for growth, a strain mutant for the gene-encoding enzyme B would be able to grow on medium supplemented with _____.

A) nutrient A only

B) nutrient B only

C) nutrient C only

D) nutrients A and C

C

A particular triplet of bases in the template strand of DNA is 5' AGT 3'. The corresponding codon for the mRNA transcribed is
A) 3' UCA 5'.
B) 3' UGA 5'.
C) 5' TCA 3'.
D) 3' ACU 5'.

A

Which of the following statements describes chromatin?
A) Heterochromatin is composed of DNA, whereas euchromatin is made of DNA and RNA.
B) Both heterochromatin and euchromatin are found in the cytoplasm.
C) Heterochromatin is highly condensed, whereas euchromatin is less compact.
D) Euchromatin is not transcribed, whereas heterochromatin is transcribed.

C

Telomere shortening is a problem in which types of cells?

A) only prokaryotic cells

B) only eukaryotic cells

C) cells in prokaryotes and eukaryotes

B

Which of the following cells have reduced or very little active telomerase activity?

A) most normal somatic cells

B) most normal germ cells

C) most cancer cells

A

What is a telomere?

A) the mechanism that holds two sister chromatids together

B) DNA replication during telophase

C) the site of origin of DNA replication

D) the ends of linear chromosomes

D

DNA is synthesized through a process known as _____.

A) semiconservative replication

B) conservative replication

C) translation

D) transcription

A

DNA contains the template needed to copy itself, but it has no catalytic activity in cells. What catalyzes the formation of phosphodiester bonds between adjacent nucleotides in the DNA polymer being formed?

A) ribozymes

B) DNA polymerase

C) ATP

D) deoxyribonucleotide triphosphates

B

What provides the energy for the polymerization reactions in DNA synthesis?

A) ATP

B) DNA polymerase

C) breaking the hydrogen bonds between complementary DNA strands

D) the deoxyribonucleotide triphosphate substrates

D

Refer to the figure above. What bases will be added to the primer as DNA replication proceeds? The bases should appear in the new strand in the order that they will be added starting at the 3' end of the primer.

1. A) C, A, G, C, A, G, A
2. B) T, C, T, G, C, T, G
3. C) A, G, A, C, G, A, C
4. D) G, T, C, G, T, C, T

C

DNA is synthesized through a process known as _____.

A) semiconservative replication

B) conservative replication

C) translation

D) transcription

A

You briefly expose bacteria undergoing DNA replication to radioactively labeled nucleotides. When you centrifuge the DNA isolated from the bacteria, the DNA separates into two classes. One class of labeled DNA includes very large molecules (thousands or even millions of nucleotides long), and the other includes short stretches of DNA (several hundred to a few thousand nucleotides in length). These two classes of DNA probably represent _____.

A) leading strands and Okazaki fragments

B) lagging strands and Okazaki fragments

C) Okazaki fragments and RNA primers

D) leading strands and RNA primers

A

Within a double-stranded DNA molecule, adenine forms hydrogen bonds with thymine and cytosine forms hydrogen bonds with guanine. This arrangement _____.

A) allows variable width of the double helix

B) permits complementary base pairing

C) determines the tertiary structure of a DNA molecule

D) determines the type of protein produced

B

The leading and the lagging strands differ in that _____.

1. A) the leading strand is synthesized in the same direction as the movement of the replication fork, and the lagging strand is synthesized in the opposite direction
2. B) the leading strand is synthesized by adding nucleotides to the end of the growing strand, and the lagging strand is synthesized by adding nucleotides to the end
3. C) the lagging strand is synthesized continuously, whereas the leading strand is synthesized in short fragments that are ultimately stitched together
4. D) the leading strand is synthesized at twice the rate of the lagging strand

A

A new DNA strand elongates only in the 5' to 3' direction because _____.

1. A) DNA polymerase begins adding nucleotides at the 5' end of the template
2. B) the polarity of the DNA molecule prevents addition of nucleotides at the 3' end
3. C) replication must progress toward the replication fork
4. D) DNA polymerase can add nucleotides only to the free 3' end

D

What is the function of topoisomerase?

A) relieving strain in the DNA ahead of the replication fork

B) elongating new DNA at a replication fork by adding nucleotides to the existing chain

C) unwinding of the double helix

D) stabilizing single-stranded DNA at the replication fork

A

What is the role of DNA ligase in the elongation of the lagging strand during DNA replication?

A) It synthesizes RNA nucleotides to make a primer.

B) It joins Okazaki fragments together.

C) It unwinds the parental double helix.

D) It stabilizes the unwound parental DNA.

B

In E. coli, to repair a thymine dimer by nucleotide excision repair, in which order do the necessary enzymes act?

A) nuclease, DNA polymerase III, RNA primase

B) helicase, DNA polymerase I, DNA ligase

C) DNA ligase, nuclease, helicase

D) nuclease, DNA polymerase I, DNA ligase

D

Replication in prokaryotes differs from replication in eukaryotes for which of the following reasons?

A) Prokaryotic chromosomes have histones, whereas eukaryotic chromosomes do not.

B) Prokaryotic chromosomes have a single origin of replication, whereas eukaryotic chromosomes have many.

C) The rate of elongation during DNA replication is slower in prokaryotes than in eukaryotes.

D) Prokaryotes produce Okazaki fragments during DNA replication, but eukaryotes do not.

B

What is meant by the description "antiparallel" regarding the strands that make up DNA?

1. A) The twisting nature of DNA creates nonparallel strands.
2. B) The 5' to 3' direction of one strand runs counter to the to direction of the other strand.
3. C) Base pairings create unequal spacing between the two DNA strands.
4. D) One strand contains only purines and the other contains only pyrimidines.

B

Suppose you are provided with an actively dividing culture of E. coli bacteria to which radioactive thymine has been added. What would happen if a cell replicates once in the presence of this radioactive base?

A) One of the daughter cells, but not the other, would have radioactive DNA.

B) Neither of the two daughter cells would be radioactive.

C) All four bases of the DNA would be radioactive.

D) DNA in both daughter cells would be radioactive.

D

In E. coli, there is a mutation in a gene called dnaB that alters the helicase that normally acts at the origin. Which of the following would you expect as a result of this mutation?

A) Additional proofreading will occur.

B) No replication fork will be formed.

C) Replication will occur via RNA polymerase alone.

D) Replication will require a DNA template from another source.

B

In E. coli, which enzyme catalyzes the elongation of a new DNA strand in the → direction?

1. A) primase
2. B) DNA ligase
3. C) DNA polymerase III
4. D) helicase

C

Eukaryotic telomeres replicate differently than the rest of the chromosome. This is a consequence of which of the following?

1. A) the evolution of telomerase enzyme
2. B) DNA polymerase that cannot replicate the leading strand template to its 5' end
3. C) gaps left at the 5' end of the lagging strand
4. D) gaps left at the 3' end of the lagging strand because of the need for a primer

C

How does the enzyme telomerase meet the challenge of replicating the ends of linear chromosomes?

1. A) It adds a single cap structure that resists degradation by nucleases.
2. B) It causes specific double-strand DNA breaks that result in blunt ends on both strands.
3. C) It catalyzes the lengthening of telomeres, compensating for the shortening that could occur during replication without telomerase activity.
4. D) It adds numerous GC pairs, which resist hydrolysis and maintain chromosome integrity.

C

Hershey and Chase set out to determine what molecule served as the unit of inheritance. They completed a series of experiments in which E. coli was infected by a T2 virus. Which molecular component of the T2 virus actually ended up inside the cell?

A) protein

B) RNA

C) ribosome

D) DNA

D

Cytosine makes up 42% of the nucleotides in a sample of DNA from an organism. Approximately what percentage of the nucleotides in this sample will be thymine?

A) 8%

B) 16%

C) 42%

D) 58%

A

It became apparent to Watson and Crick after completion of their model that the DNA molecule could carry a vast amount of hereditary information in which of the following?

A) sequence of bases

B) phosphate-sugar backbones

C) complementary pairing of bases

D) side groups of nitrogenous bases

A

In an analysis of the nucleotide composition of DNA, which of the following will be found?

A) A = C

B) A = G and C = T

C) A + C = G + T

D) G + C = T + A

C

How do we describe transformation in bacteria?

A) the creation of a strand of DNA from an RNA molecule

B) the creation of a strand of RNA from a DNA molecule

C) the infection of cells by a phage DNA molecule

D) assimilation of external DNA into a cell

D

After mixing a heat-killed, phosphorescent (light-emitting) strain of bacteria with a living, nonphosphorescent strain, you discover that some of the living cells are now phosphorescent. Which observation(s) would provide the best evidence that the ability to phosphoresce is a heritable trait?

A) evidence that DNA was passed from the heat-killed strain to the living strain

B) evidence that protein passed from the heat-killed strain to the living strain

C) especially bright phosphorescence in the living strain

D) phosphorescence in descendants of the living cells

D

In trying to determine whether DNA or protein is the genetic material, Hershey and Chase made use of which of the following facts?

A) DNA contains sulfur, whereas protein does not.

B) DNA contains phosphorus, whereas protein does not.

C) DNA contains nitrogen, whereas protein does not.

D) DNA contains purines, whereas protein includes pyrimidines.

B

What is a syndrome?
A) a characteristic facial appearance
B) a group of traits, all of which must be present if an aneuploidy is to be diagnosed
C) a group of traits typically found in conjunction with a particular chromosomal aberration or gene mutation
D) a characteristic trait usually given the discoverer's name

C

One possible result of chromosomal breakage is for a fragment to join a nonhomologous chromosome. What is this alteration called?
A) deletion
B) transversion
C) inversion
D) translocation

D

What is the reason that closely linked genes are typically inherited together?

A) They are located close together on the same chromosome.

B) The number of genes in a cell is greater than the number of chromosomes.

C) Alleles are paired together during meiosis.

D) Genes align that way during metaphase I of meiosis.

A

In Drosophila melanogaster, vestigial wings are caused by a recessive allele of a gene that is linked to a gene with a recessive allele that causes black body color. Morgan crossed black-bodied, normal-winged females and gray-bodied, vestigial-winged males. The F1 were all gray bodied, normal winged. The F1 females were crossed to homozygous recessive males to produce testcross progeny. Morgan calculated the map distance to be 17 map units. Which of the following is correct about the testcross progeny?

A) black-bodied, normal-winged flies = 17% of the total

B) black-bodied, normal-winged flies PLUS gray-bodied, vestigial-winged flies = 17% of the total

C) gray-bodied, normal-winged flies PLUS black-bodied, vestigial-winged flies = 17% of the total

D) black-bodied, vestigial-winged flies = 17% of the total

C

Recombination between linked genes comes about for what reason?
A) Nonrecombinant chromosomes break and then rejoin with one another.
B) Independent assortment sometimes fails.
C) Linked genes travel together at anaphase.
D) Crossovers between these genes result in chromosomal exchange.

D

Map units on a linkage map cannot be relied upon to calculate physical distances on a chromosome for which of the following reasons?

A) The frequency of crossing over varies along the length of the chromosome.

B) The relationship between recombination frequency and map units is different in every individual.

C) Physical distances between genes change during the course of the cell cycle.

D) The gene order on the chromosomes is slightly different in every individual.

A

Between which two genes would you expect the highest frequency of recombination?

A) A and W

B) E and G

C) A and E

D) A and G

D

Sturtevant provided genetic evidence for the existence of four pairs of chromosomes in Drosophila in which of these ways?

A) There are four major functional classes of genes in Drosophila.

B) Drosophila genes cluster into four distinct groups of linked genes.

C) The overall number of genes in Drosophilais a multiple of four.

D) Drosophila genes have, on average, four different alleles.

B

Which of the following statements is true of linkage?

A) The closer two genes are on a chromosome, the lower the probability that a crossover will occur between them.

B) The observed frequency of recombination of two genes that are far apart from each other has a maximum value of 100%.

C) All of the traits that Mendel studied—seed color, pod shape, flower color, and others—are due to genes linked on the same chromosome.

D) Linked genes are found on different chromosomes.

A

How would one explain a testcross involving F1 dihybrid flies in which more parental-type offspring than recombinant-type offspring are produced?

A) The two genes are closely linked on the same chromosome.

B) The two genes are linked but on different chromosomes.

C) Recombination did not occur in the cell during meiosis.

D) Both of the characters are controlled by more than one gene.

A

What does a frequency of recombination of 50% indicate?

A) The two genes are likely to be located on different chromosomes.

B) All of the offspring have combinations of traits that match one of the two parents.

C) The genes are located on sex chromosomes.

D) Abnormal meiosis has occurred.

A

A man who carries an allele of an X-linked gene will pass it on to _____.

A) all of his daughters

B) half of his daughters

C) all of his sons

D) all of his children

A

Glucose-6-phosphate dehydrogenase deficiency (G6PD) is inherited as a recessive allele of an X-linked gene in humans. A woman whose father suffered from G6PD marries a normal man.

(a) What proportion of their sons is expected to be G6PD?

(b) If the husband was not normal but was G6PD deficient, would you change your answer in part (a)?

A) (a) 100%; (b) no

B) (a) 1/2; (b) yes

C) (a) 1/2; (b) no

D) (a) zero; (b) no

C

A mutant bacterial cell has a defective aminoacyl synthetase that attaches a lysine to tRNAs with the anticodon AAA instead of the normal phenylalanine. The consequence of this for the cell will be that
A) none of the proteins in the cell will contain phenylalanine.
B) proteins in the cell will include lysine instead of phenylalanine at amino acid positions specified by the codon UUU.
C) the cell will compensate for the defect by attaching phenylalanine to tRNAs with lysine-specifying anticodons.
D) the ribosome will skip a codon every time a UUU is encountered.

B

There are 61 mRNA codons that specify an amino acid, but only 45 tRNAs. This is best explained by the fact that
A) some tRNAs have anticodons that recognize four or more different codons.
B) the rules for base pairing between the third base of a codon and tRNA are flexible.
C) many codons are never used, so the tRNAs that recognize them are dispensable.
D) the DNA codes for all 61 tRNAs but some are then destroyed.

B

The release factor (RF) _____.

A) binds to the stop codon in the A site in place of a tRNA

B) releases the amino acid from its tRNA to allow the amino acid to form a peptide bond

C) supplies a source of energy for termination of translation

D) releases the ribosome from the ER to allow polypeptides into the cytosol

A

The anticodon loop of the first tRNA that will complement this mRNA is

A) GGC

B) GGC

C) UGC

D) UGC

A

What type of bonding is responsible for maintaining the shape of the tRNA molecule shown in the figure above?

A) ionic bonding between phosphates

B) hydrogen bonding between base pairs

C) van der Waals interactions between hydrogen atoms

D) peptide bonding between amino acids

B

The figure above represents tRNA that recognizes and binds a particular amino acid (in this instance, phenylalanine). Which codon on the mRNA strand codes for this amino acid?

A) UGG

B) GUG

C) GUA

D) UUC

D

The tRNA shown in the figure above has its end projecting beyond its end. What will occur at this end?

A) The amino acid binds covalently.

B) The excess nucleotides (ACCA) will be cleaved off at the ribosome.

C) The small and large subunits of the ribosome will attach to it.

D) The cap of the mRNA will become covalently bound.

A

Translation requires _____.

A) mRNA, tRNA, DNA, and rRNA

B) mRNA, DNA, and rRNA

C) mRNA, tRNA, and rRNA

D) mRNA, tRNA, and DNA

C

Once a peptide has been formed between the amino acid attached to the tRNA in the P site and the amino acid associated with the tRNA in the A site, what occurs next?

A) translocation

B) reading of the next codon of mRNA

C) initiation

D) The codon-anticodon hydrogen bonds holding the tRNA in the A site are broken.

A

Which one of the following, if missing, would usually prevent translation from starting?

A) exon

B) cap

C) AUG codon

D) poly-A tail

C

) Put the following events of elongation in prokaryotic translation in chronological order.

1. Binding of mRNA with small ribosomal subunit

2. Recognition of initiation codon

3. Complementary base pairing between initiator codon and anticodon of initiator tRNA

4. Base pairing of the mRNA codon following the initiator codon with its complementary tRNA

5. Attachment of the large subunit

A) 1, 2, 3, 4, 5

B) 2, 1, 4, 3, 5

C) 5, 4, 3, 2, 1

D) 1, 2, 3, 5, 4

D

How does termination of translation take place?

A) The end of the mRNA molecule is reached.

B) A stop codon is reached.

C) The cap is reached.

D) The poly-A tail is reached.

B

Post-translational modifications of proteins may include the _____.

A) removal of introns

B) addition of a 5’ cap

C) addition of a poly-A tail

D) addition of carbohydrates to form a glycoprotein

D

During elongation, which site in the ribosome represents the location where a codon is being read?

A) E site

B) P site

C) A site

D) the small ribosomal subunit

C

What must occur before a newly made polypeptide is secreted from a cell?

A) It must be translated by a ribosome that remains free within the cytosol.

B) Its signal sequence must target it to the ER, after which it goes to the Golgi.

C) Its signal sequence must be cleaved off before the polypeptide can enter the ER.

D) Its signal sequence must target it to the plasma membrane, where it causes exocytosis.

B

The dipeptide that will form will be
A) cysteine-alanine.
B) proline-threonine.
C) glycine-cysteine.
D) alanine-alanine.
E) threonine-glycine

B

Which of the following is the first event to take place in translation in eukaryotes?
A) elongation of the polypeptide
B) base pairing of activated methionine-tRNA to AUG of the messenger RNA
C) binding of the larger ribosomal subunit to smaller ribosomal subunits
D) covalent bonding between the first two amino acids
E) the small subunit of the ribosome recognizes and attaches to the 5' cap of mRNA

E

Which of the following is a function of a signal peptide?
A) to direct an mRNA molecule into the cisternal space of the ER
B) to bind RNA polymerase to DNA and initiate transcription
C) to terminate translation of the messenger RNA
D) to translocate polypeptides across the ER membrane

D

Which of the following statements is true about protein synthesis in prokaryotes?
A) Extensive RNA processing is required before prokaryotic transcripts can be translated.
B) Translation can begin while transcription is still in progress.
C) Prokaryotic cells have complicated mechanisms for targeting proteins to the appropriate cellular organelles.
D) Translation requires antibiotic activity.
E) Unlike eukaryotes, prokaryotes require no initiation or elongation factors.

B

The most commonly occurring mutation in people with cystic fibrosis is a deletion of a single codon. This results in
A) a base-pair substitution.
B) a nucleotide mismatch.
C) a frameshift mutation.
D) a polypeptide missing an amino acid.
E) a nonsense mutation.

D

How might a single base substitution in the sequence of a gene affect the amino acid sequence of a protein encoded by the gene, and why?

A) Only a single amino acid could change, because the reading frame is unaffected.

B) The amino acid sequence would be substantially altered, because the reading frame would change with a single base substitution.

C) All amino acids following the substitution would be affected, because the reading frame would be shifted.

D) It is not possible for a single base substitution to affect protein structure, because each codon is three bases long.

A

What do we mean when we use the terms monohybrid cross and dihybrid cross?

A) A monohybrid cross involves a single parent, whereas a dihybrid cross involves two parents.
B) A monohybrid cross produces a single progeny, whereas a dihybrid cross produces two progeny.
C) A dihybrid cross involves organisms that are heterozygous for two characters and a monohybrid cross involves only one.
D) A monohybrid cross is performed for one generation, whereas a dihybrid cross is performed for two generations.
E) A monohybrid cross results in a 9:3:3:1 ratio whereas a dihybrid cross gives a 3:1 ratio.

C

The fact that all seven of the pea plant traits studied by Mendel obeyed the principle of independent assortment most probably indicates which of the following?

A) None of the traits obeyed the law of segregation.
B) The diploid number of chromosomes in the pea plants was 7.
C) All of the genes controlling the traits were located on the same chromosome.
D) All of the genes controlling the traits behaved as if they were on different chromosomes.

D

Which of the boxes marked 1-4 correspond to plants with dark leaves?
A) 1 only
B) 1 and 2
C) 2 and 3
D) 4 only
E) 1, 2, and 3

E

Albinism is an autosomal (not sex-linked) recessive trait. A man and woman are both of normal pigmentation and have one child out of three who is albino (without melanin pigmentation). What are the genotypes of the albino's parents?

A) One parent must be homozygous for the recessive allele; the other parent can be homozygous dominant, homozygous recessive, or heterozygous.

B) One parent must be heterozygous; the other parent can be homozygous dominant, homozygous recessive, or heterozygous.

C) Both parents must be heterozygous.

D) One parent must be homozygous dominant; the other parent must be heterozygous.

C

Black fur in mice (B) is dominant to brown fur (b). Short tails (T) are dominant to long tails (t). What fraction of the progeny of crosses BbTt . BBtt will be expected to have black fur and long tails?

A) 1/16

B) 3/8

C) 1/2

D) 9/16

C

A woman who has blood type A positive has a daughter who is type O positive and a son who is type B negative. Rh positive is a trait that shows simple dominance over Rh negative. Which of the following is a possible phenotype for the father?

A) A negative

B) O negative

C) B positive

D) AB negative

C

In humans, ABO blood types refer to glycoproteins in the membranes of red blood cells. There are three alleles for this autosomal gene: IA, IB, and i. The IA allele codes for the A glycoprotein, The IB allele codes for the B glycoprotein, and the i allele doesn't code for any membrane glycoprotein. IA and IB are codominant, and i is recessive to both IA and IB. People with type A blood have the genotypes IAIA or IAi, people with type B blood are IBIB or IBi, people with type AB blood are IAIB, and people with type O blood are ii. If a woman with type AB blood marries a man with type O blood, which of the following blood types could their children possibly have?

A) A and B

B) AB and O

C) A, B, and O

D) A, B, AB, and O

A

What is the genotype of individual II-5?
A) WW
B) Ww
C) ww
D) WW or ww
E) ww or Ww

C

What is the likelihood that the progeny of IV-3 and IV-4 will have the trait?
A) 0%
B) 25%
C) 50%
D) 75%
E) 100%

C

What is the probability that individual III-1 is Ww?
A) 3/4
B) 1/4
C) 2/4
D) 2/3
E) 1

E

From this pedigree, how does this trait seem to be inherited?
A) from mothers
B) as an autosomal recessive
C) as a result of epistasis
D) as an autosomal dominant

D

Which of the following statements is a correct explanation for the observation that all offspring exhibit a phenotype for a particular trait that appears to be a blend of the two parental varieties?

A) Neither of the parental genes is dominate over the other.

B) The genes for the trait are dominant in both of the parents.

C) The genes are linked and do not separate during meiosis.

D) The genes for the trait are recessive in both of the parents.

A

) A gene for the MN blood group has codominant alleles Mand N. If both children are of blood type M, which of the following is possible?

A) Each parent is either M or MN.

B) Each parent must be type M.

C) Both children are heterozygous for this gene.

D) Neither parent can have the N allele.

A

In certain plants, tall is dominant to short. If a heterozygous plant is crossed with a homozygous tall plant, what is the probability that the offspring will be short?

A) 1

B) 1/2

C) 1/4

D) 0

D

In the cross AaBbCc . AaBbCc, what is the probability of producing the genotype AABBCC?

A) 1/4

B) 1/8

C) 1/16

D) 1/64

D

A black guinea pig crossed with an albino guinea pig produced twelve black offspring. When the albino was crossed with a second black animal, six blacks and six albinos were obtained. What is the best explanation for this genetic situation?

A) Albino is recessive; black is dominant.

B) Albino is dominant; black is incompletely dominant.

C) Albino and black are codominant.

D) Albino is recessive; black is codominant.

A

Gray seed color in peas is dominant to white. Assume that Mendel conducted a series of experiments where plants with gray seeds were crossed among themselves, and the following progeny were produced: 302 gray and 98 white.

(a) What is the most probable genotype of each parent?

(b) Based on your answer in (a) above, what genotypic and phenotypic ratios are expected in these progeny? (Assume the following symbols: G = gray and g = white.)

A) (a) GG . gg; (b) genotypic = 3:1, phenotypic = 1:2:1

B) (a) Gg . Gg; (b) genotypic = 1:2:1, phenotypic = 3:1

C) (a) GG . Gg; (b) genotypic = 1:2:1, phenotypic = 2:1

D) (a) gg . Gg; (b) genotypic = 1:2, phenotypic = 3:1

B

Which of the boxes marked 1-4 correspond to plants with a heterozygous genotype?

A) 1

B) 1, 2, and 3

C) 2 and 3

D) 2, 3, and 4

C

Which of the boxes marked 1-4 correspond to plants that will be true-breeding?

A) 1 and 4 only

B) 2 and 3 only

C) 1, 2, 3, and 4

D) 1 only

A

Skin color in a certain species of fish is inherited via a single gene with four different alleles. How many different types of gametes would be possible in this system?

A) 2

B) 4

C) 8

D) 16

B

Mendel's observation of the segregation of alleles in gamete formation has its basis in which of the following phases of cell division?
A) prophase I of meiosis
B) anaphase II of meiosis
C) metaphase I of meiosis
D) anaphase I of meiosis

D

What was the most significant conclusion that Gregor Mendel drew from his experiments with pea plants?

A) There is considerable genetic variation in garden peas.
B) Traits are inherited in discrete units, and are not the results of "blending."
C) Recessive genes occur more frequently in the F₁ generation than do dominant ones.
D) Genes are composed of DNA.

B

The individual with genotype AaBbCCDdEE can make many kinds of gametes. Which of the following is the major reason?
A) segregation of maternal and paternal alleles
B) recurrent mutations forming new alleles
C) crossing over during prophase I
D) different possible alignments of chromosomes

D

Why did Mendel continue some of his experiments to the F₂ or F₃ generation?

A) to obtain a larger number of offspring on which to base statistics
B) to observe whether or not a recessive trait would reappear
C) to observe whether or not the dominant trait would reappear
D) to distinguish which alleles were segregating

B

Which of the following statements about independent assortment and segregation is correct?

A) The law of independent assortment requires describing two or more genes relative to one another.

B) The law of segregation requires describing two or more genes relative to one another.

C) The law of independent assortment is accounted for by observations of prophase I.

D) The law of segregation is accounted for by anaphase of mitosis.

A

A sexually reproducing animal has two unlinked genes, one for head shape (H) and one for tail length (T). Its genotype is HhTt. Which of the following genotypes is possible in a gamete from this organism?

A) Hh

B) HhTt

C) T

D) HT

D

An original section of DNA has the base sequence AGCGTTACCGT. A mutation in this DNA strand results in the base sequence AGGCGTTACCGT. This change represents _____.

A) a missense mutation

B) a point mutation

C) a silent mutation

D) frameshift mutation

D

A single base substitution mutation is least likely to be deleterious when the base change results in _____.

A) a stop codon

B) a codon that specifies the same amino acid as the original codon

C) an amino acid substitution that alters the tertiary structure of the protein

D) an amino acid substitution at the active site of an enzyme

B

Rank the following one-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 third position of an exonic codon

3. substitution mutation at the second position of an exonic codon

4. deletion mutation within the first exon of the gene

A) 1, 2, 3, 4

B) 4, 3, 2, 1

C) 2, 1, 4, 3

D) 3, 1, 4, 2

B

Of the following, which is the most current description of a gene?

A) a unit of heredity that causes formation of a phenotypic characteristic

B) a DNA subunit that codes for a single complete protein

C) a DNA sequence that is expressed to form a functional product: either RNA or polypeptide

D) a discrete unit of hereditary information that consists of a sequence of amino acids

C

Which of the following types of mutation, resulting in an error in the mRNA just after the AUG start of translation, is likely to have the most serious effect on the polypeptide product?

A) a deletion of a codon

B) a deletion of two nucleotides

C) a substitution of the third nucleotide in an ACC codon

D) a substitution of the first nucleotide of a GGG codon

B

A nonsense mutation in a gene _____.

A) changes an amino acid in the encoded protein

B) has no effect on the amino acid sequence of the encoded protein

C) introduces a premature stop codon into the mRNA

D) alters the reading frame of the mRNA

C

Which of the following DNA mutations is most likely to damage the protein it specifies?

A) a base-pair deletion

B) an addition of three nucleotides

C) a substitution in the last base of a codon

D) a codon deletion

A