Chapter 19

Which of the following elements would be considered to be a complete transposable element? A) An insertion sequence that includes a transposase gene between the inverted repeats. B) A composite element that carries an antibiotic resistance gene. C) A replicative transposon that includes a reverse transcriptase gene. D) A retrotransposon containing long terminal repeats.

A) An insertion sequence that includes a transposase gene between the inverted repeats.

After identification of the first "mutable site", McClintock was able to demonstrate that the element that caused the mutable site was able to move. What was her evidence? A) In some offspring from the original strain, the breakpoint was in a different location. B) In some offspring from the original strain, the phenotype was no longer mutable. C) In some offspring from the original strain, the Ac element had been lost. D) Some strains had breakpoints in different locations than other strains.

A) In some offspring from the original strain, the breakpoint was in a different location.

In transposon tagging: A) Insertion of a transposon randomly inactivates a gene of interest. B) Transposable elements are directed to inactivate a specific gene. C) Presence of a transposon in a known gene allows the cloning of the transposon. D) All of these. E) None of these.

A) Insertion of a transposon randomly inactivates a gene of interest.

By what process is the λ viral DNA inserted into the E. coli chromosome during lysogeny? A) Site specific recombination. B) Homologous recombination. C) Integral ligation. D) Strand invasion. E) None of these.

A) Site specific recombination.

Crossing over occurs in both mitosis and meiosis. A) True B) False

A) True

Retrotransposons replicate themselves during transposition. A) True B) False

A) True

What is gene conversion? A) A process by which a gene is rendered nonfunctional. B) A process that changes an allele to the allele existing on the homologous chromosome. C) A process that restores the wild type function of a gene. D) A process that creates a new allele of a gene. E) None of these.

B) A process that changes an allele to the allele existing on the homologous chromosome.

The existence of single Holliday junctions is strong support for the Holliday model of recombination. A) True B) False

B) False

Considering the steps listed below, identify the correct sequence of events proposed by the double-strand break model of recombination. I. Strand invasion and D loop formation. II. DNA gap repair synthesis. III. Generation of single stranded DNA segments. IV. Resolution. A) I, III, II, IV B) III, I, II, IV C) III, II, I, IV D) IV, III, I, II

B) III, I, II, IV

Which of the following describes the key difference between simple transposition and replicative transposition? A) In simple transposition, transposase catalyzes the removal and reintegration of the transposon, while transposase is not involved in replicative transposition. B) In simple transposition, a double stranded piece of DNA is moved from one site to another, while in replicative transposition a single strand is moved, leaving a single strand behind. C) Simple transposition requires DNA synthesis while replicative transposition does not. D) Replicative transposition requires DNA synthesis while simple transposition does not.

B) In simple transposition, a double stranded piece of DNA is moved from one site to another, while in replicative transposition a single strand is moved, leaving a single strand behind.

Barbara McClintock noted that, in a particular strain of corn, chromosome 9 tended to break at the same site at a relatively high rate. What caused this breakage? A) Random double stranded breaks. B) Inaccurate excision of a transposable element. C) Insertion of a transposable element. D) Holliday junctions.

B) Inaccurate excision of a transposable element.

What would you predict would happen if the inverted repeats at one end of a composite transposon were involved in simple transposition, rather than the two repeats at the ends? A) The rest of the transposon would be eliminated. B) The intervening sequence would be "stranded" and no longer able to move. C) The second pair of inverted repeats would be highly likely to jump out. D) All of these. E) None of these.

B) The intervening sequence would be "stranded" and no longer able to move.

Why is transposon tagging easier for X linked genes? A) These genes are more likely to have an interesting phenotype. B) These genes are hemizygous in males. C) The transposon is more likely to insert into sites on the X chromosome. D) The X chromosome does not undergo recombination.

B) These genes are hemizygous in males.

Which of these describes a Holliday junction? A) A section of DNA where base pairing is not exact. B) A strand of DNA containing genetic material from two different chromosomes. C) An interaction of two strands of DNA from homologous chromosomes. D) A three stranded DNA structure where single stranded DNA has invaded a double helix.

C) An interaction of two strands of DNA from homologous chromosomes.

In a modification of transposon tagging known as enhancer trapping, reporter gene coding regions with a minimal promoter but no regulatory elements are placed inside a composite transposon, which is then "jumped" into the chromosomes. Activation of the reporter gene in a specific tissue: A) Is unlikely to occur due to the flanking elements of the transposon. B) Indicates that the transposon has disrupted a gene whose function is critical for correct function of that tissue. C) Indicates that the transposon has integrated near tissue specific regulatory elements. D) Is likely to be recessive and thus difficult to identify.

C) Indicates that the transposon has integrated near tissue specific regulatory elements.

After isomerization and resolution, the resulting chromosomes are: A) Unchanged from the original chromosome. B) Nonrecombinant chromosomes with a heteroduplex region. C) Recombinant chromosomes with a heteroduplex region. D) Recombinant chromosomes without a heteroduplex region. E) Harlequin chromosomes.

C) Recombinant chromosomes with a heteroduplex region.

Which type of transposable element is only found in eukaryotes (not prokaryotes)? A) Transposable elements that move by simple transposition. B) Transposable elements that move by replicative transposition. C) Retrotransposons, which move via an RNA intermediate. D) All of these. E) None of these.

C) Retrotransposons, which move via an RNA intermediate.

Which statement regarding recombination is false? A) Recombination creates new combinations of alleles on a chromosome. B) Recombination commonly occurs between homologous sequences. C) Sister chromatid exchange is a form of recombination. D) Gene conversion may occur during recombination.

C) Sister chromatid exchange is a form of recombination.

In exon shuffling, a new exon may be inserted into a gene via transposition, leading to a protein with a modified function. Which of these statements is most likely to be true? A) The new exon is probably inserted into an existing exon. B) The new exon changes the reading frame of the original protein. C) The new exon is probably inserted into an intron. D) All of the above are likely to be true. E) None of the above are likely to be true.

C) The new exon is probably inserted into an intron.

Composite transposons can be recognized by which of the following characteristics? A) Inverted repeats. B) Direct repeats. C) Two pairs of inverted repeats flanking an intervening gene. D) Two pairs of direct repeats flanking a transposase gene.

C) Two pairs of inverted repeats flanking an intervening gene.

Antibodies are: A) Proteins produced by the immune system. B) Able to bind specifically to a single antigen. C) An example of proteins with quaternary structure. D) All of the above. E) None of the above.

D) All of the above.

Harlequin chromosomes A) Have been used to demonstrate sister chromatid exchange. B) Have sister chromatids that stain differently. C) Can only exist in prophase or metaphase. D) All of the above. E) None of the above.

D) All of the above.

If double stranded break recombination and DNA gap repair synthesis result in gene conversion, how is the original allele lost? A) It isn't, it is merely rearranged. B) It is eliminated by DNA repair enzymes. C) It is prevented from replication due to selective pressure. D) It is digested away after a break within the gene.

D) It is digested away after a break within the gene.

Which of these mechanisms is NOT critical to generation of antibody variability? A) Site specific recombination. B) Presence of many V and J regions in a single gene. C) Imprecise joining at recombination signal sequences. D) All of the above. E) None of the above.

E) None of the above.

Simple transposons do not replicate themselves during transposition but they are able to proliferate. How? A) They are replicated after excision from the DNA strand, creating extra copies to be inserted at new sites. B) Excision is stimulated by DNA repair processes. C) These transposons separate into single stranded elements after excision. Insertion of two single strands followed by DNA gap repair effectively duplicates the element. D) All of these. E) None of these.

E) None of these.