1. Which of the following facts would NOT be considered as an advantage for using bacteria and viruses for genetic studies?
A) Rapid reproduction and high progeny number
B) Haploid genome for expressing mutations
C) Complete absence of recombination, which maintains the integrity of genome
D) Low cost to maintain and little storage space required
E) Genomes being small and readily subjected to genetic manipulation
2. Bacterial mutants that require supplemental nutrients in their growth media are called:
A) autotrophs.
B) heterotrophs.
C) prototrophs.
D) omnitrophs.
E) auxotrophs.
3. Which of the following statements about nutritional requirement and growth of bacteria is NOT true?
A) Culture media developed for bacteria must contain carbon source and essential elements for the survival of the bacteria.
B) Auxotrophic mutants can grow on medium that lack carbon source because they can synthesize their own nutrients.
C) Each bacterium has specific nutritional needs and conditions for successful cultivation.
D) Prototrophic bacterial strains can grow on minimal media.
E) The growth rate of bacteria on specific media can be assessed by the number and size of bacterial colonies.
4. Bacterial strains that can produce all the necessary compounds and therefore grow on minimal media are called:
A) autotrophs.
B) heterotrophs.
C) prototrophs.
D) omnitrophs.
E) auxotrophs.
5. _____ medium contains all of the substances required by bacteria for growth and reproduction.
A) Minimal
B) Complete
C) Auxotrophic
D) Selective
E) Liquid
6. _____ solidifies when cooled and provides a solid, gel-like base for bacterial growth.
A) Broth
B) Agar
C) Colony
D) Liquid
E) Velvet
7.
_____ is used to isolate mutant bacterial strains on the basis of their nutritional requirements.
A) Autoclaving
B) Complete medium
C) Replica plating
D) Karyotyping
E) Conjugation
8. Which of the following statements about bacterial genome is NOT true?
A) All bacteria contain a single circular double-stranded DNA as their genome.
B) Some bacteria may have linear chromosomes instead of circular.
C) In addition to chromosomes, many bacteria possess small extrachromosomal DNA called plasmids.
D) Each plasmid contains an origin of replication that allows independent replication for its maintenance.
E) The F factor, which is important for bacterial conjugation, is found as a circular episome of E. coli.
9. Which of the following refers to a slender extension of the cell membrane used for bacterial conjugation?
A) episome
B) F factor
C) pilus
D) prophage
E) oncogene
10. What happens to the remainder of the donated chromosome after crossing over has taken place in the recipient cell?
A) It is not maintained and is degraded.
B) It is replicated and kept as an episome.
C) It is transferred to another bacterium via conjugation.
D) It is integrated into the nucleus.
E) Nothing happens to it, so it just floats around in the cytoplasm.
11. Bacterial cells containing an F plasmid that has acquired bacterial chromosomal genes are called:
A) F+ .
B) F .
C) F–.
D) Hfr.
E) Hfr+ .
12. A bacterial cell transfers chromosomal genes to F– cells, but it rarely causes them to become F+. The bacterial cell is:
A) Hfr.
B) lysogenic.
C) auxotrophic.
D) lytic.
E) F+
13. Which of the following statements about genetic exchange in bacteria is NOT true?
A) Bacteria do not always require direct DNA transfer from other living cells in order to acquire genetic material.
B) Plasmids do not have to integrate into the host cell chromosome in order to be replicated.
C) Interrupted conjugation results in the production of Hfr strains.
D) The order of gene transfer is not the same for different Hfr strains.
E) Antibiotic resistance can be transferred from one bacterial cell to another by conjugation.
14. Conjugation between an F cell and an F– cell may produce partial diploids called _____.
A) homozygotes
B) heterozygotes
C) hemizygotes
D) pseudozygotes
E) merozygotes
15. Which of the following will have the LEAST influence on the efficiency of transformation in E. coli bacteria?
A) Calcium chloride treatment
B) Heat shock
C) Electrical field
D) Chilling on the ice
E) The amount of foreign DNA
16. Which of the following gene transfer mechanisms would specifically use time as a basic unit of mapping?
A) Transformation
B) Crossing over
C) Transduction
D) Conjugation
E) Recombination
17. The transfer of DNA from a donor cell to a recipient cell through a cytoplasmic connection is called:
A) transformation.
B) transduction.
C) lysogenic cycle.
D) lytic cycle.
E) conjugation.
18. When the F factor episome integrates into the E. coli chromosome, the result is which of the following strains?
A) Hfr
B) F–
C) F+
D) F
E) F+/–
19. Cotransformation between two genes is more likely if they are:
A) close to one another.
B) far apart from one another.
C) separated by the F factor.
D) both oriented in the same direction.
E) not located on the same chromosome.
20. Which of the following statements about antibiotic resistance in bacteria is NOT true?
A) Antibiotic resistance cannot be conferred by conjugation as conjugation only affects the fertility of bacteria.
B) The antibiotic resistance gene can be transmitted to bacteria via transformation or transduction.
C) Environments where antibiotics are frequently used such as hospitals are under the higher risk of developing antibiotic resistance.
D) Antibiotic resistance often originates from the microbes that produce antibiotics for their own survival.
E) The plasmid containing the antibiotic resistance gene can pass the genes to genetically unrelated bacteria.
21. Joshua Lederberg and Edward Tatum conducted experiments with two auxotrophic strains of E. coli. The Y20 strain had the genotype thr– leu– thi– bio+ phe+ cys +, and the Y24 strain had the genotype thr+ leu+ thi+ bio– phe–cys –. Which of the following procedures would produce growth of bacterial colonies?
A) Spread the Y20 strain on minimal medium agar plates.
B) Spread the Y24 strain on minimal medium agar plates.
C) Boil the Y20 strain, and spread it on minimal medium agar plates.
D) Boil the Y24 strain, and spread it on minimal medium agar plates.
E) Mix the Y20 and Y24 strains together, and spread it on minimal medium agar plates.
22. What is the result of conjugation between F and F– cells?
A) One F+ cells
B) Two F cells
C) Two F+ cells
D) One Hfr and one F– cells
E) Two Hfr cells
23. leu– bacteria are mixed in a flask with leu+ bacteria, and soon all bacteria are leu+ . However, if the leu– cells are on one side of a U-tube and the leu+ cells are on the other, the leu– cells do not become prototrophic. Which process is likely to produce this observed result?
A) Conjugation
B) Transduction
C) Transformation
D) Reciprocal translocation
E) Transfection
24. How are Hfr strains of bacteria different from F+ strains?
A) Cells of Hfr strains are able to transfer chromosomal genes, whereas cells of F+ strains cannot.
B) Cells of Hfr strains cannot initiate conjugation with F– cells.
C) The F factor is integrated into the bacterial chromosome in all or most cells of an Hfr strain but in only a few cells in an F+ strain.
D) Cells of Hfr strains carry F plasmids, whereas F+ cells do not.
E) Cells of Hfr strains can initiate conjugation with F+ cells or other Hfr cells.
25. You perform interrupted-mating experiments on three Hfr strains (A, B, and C). Genes are transferred (from last to first) in the following order from each strain: strain A, thi-his-gal-lac-pro; strain B, azi-leu-thr-thi-his; strain C, lac-gal-his-thi-thr. How are the F factors in these strains oriented?
A) A and B are oriented in the same direction.
B) B and C are oriented in the same direction.
C) A and C are oriented in the same direction.
D) All of them are oriented in the same direction.
E) It cannot be determined from the information given.
26. A bacterium of genotype a +b+ c +d+ is the donor in a cotransformation mapping. The recipient is a –b–c –d–. Data from the transformed cells are shown below. What is the order of the genes?
a + and b+ 2
a + and c + 0
a + and d+ 5
b+ and c + 5
b+ and d+ 0
c + and d+ 0
A) a c b d
B) a d c b
C) c b a d
D) c a d b
E) b c d a
27. The figure below shows a partial chromosome map of an E. coli Hfr strain. Each mark equals 10 minutes. If transfer of genes begins at “*” and goes in the direction of the arrow, which of the predicted results from this map is highly likely to be observed?
A) gal will be the first, and ton will be the last gene to be transferred.
B) lac and azi will rarely be transferred together.
C) Ten minutes after transfer of ton, azi will be transferred.
D) It would take 30 minutes to transfer all of the genes that are shown.
E) All the chromosomal genes will be transferred by the end.
28. The figure below shows the results of interrupted-mating experiments with three different Hfr strains. What is the order of the genes, starting with C?
Hfr strain Order of transfer
1 A, B, E, D, F
2 D, F, C, G, A
3 D, E, B, A, G
A) C, G, A, D, F, B, E
B) C, F, D, B, A, E, G
C) C, B, E, D, F, G, A
D) C, G, A, B, E, D, F
E) C, D, F, G, A, B, E
29. Integrated, inactive, phage DNA is called a:
A) progeny.
B) prophage.
C) transformant.
D) transductant.
E) conjugate.
30. The life cycle of virulent phages that always kill their host cell and never become inactive prophages would be the _____ cycle.
A) lethal
B) lytic
C) temperate
D) strict
E) lysogenic
31. A high concentration of bacteria used to produce a continuous layer on an agar plate is called a(n):
A) bacterial lawn.
B) colony.
C) virus.
D) integrase.
E) plaque.
32. A clear patch of lysed cells on a bacterial agar plate that indicates lytic phage reproduction is called a(n):
A) plaque.
B) transformation.
C) prophage.
D) oncogene.
E) provirus.
33. The process of transferring DNA from one bacterium to another through a bacteriophage is:
A) conjugation.
B) induction.
C) transformation.
D) transduction.
E) infection.
34. Which type of transduction is used to map distances between phage genes?
A) Generalized transduction
B) Specialized transduction
C) Targeted transduction
D) Random transduction
E) Discontinuous transduction
35. Two different strains of a mutant phage infect a single bacterium. One phage strain is d–and the other is e –. Some of the progeny phages are genotype d+ e +, and some are d–e –. What genetic phenomenon does this demonstrate?
A) Complementation
B) Specialized transduction
C) Generalized transduction
D) Recombination
E) Differentiation
36. What does the enzyme reverse transcriptase do?
A) Using the amino acid sequence of a protein as a template, it makes an RNA molecule.
B) Using RNA as a template, it makes a DNA molecule.
C) Using RNA as a template, it makes an RNA molecule.
D) Using DNA as a template, it makes an RNA molecule.
E) Using DNA as a template, it makes DNA molecule.
37. Which of the following statements about retroviruses is FALSE?
A) All retroviruses contain oncogenes, which can induce the formation of tumors.
B) All retroviruses contain gag genes whose product forms the viral protein coat.
C) All retroviruses require pol genes, which are critical for retrotranscription.
D) All retroviral genomes have gag, pol, and env genes.
E) Not all RNA viruses are retroviruses.
38. HIV belongs to a group of viruses called:
A) ssDNA viruses.
B) dsDNA viruses.
C) dsDNA retroviruses.
D) ssRNA viruses.
E) ssRNA retroviruses.
39. The continual genetic change that is introduced into the influenza genome is called antigenic:
A) drift.
B) shift.
C) swing.
D) wander.
E) roam.
40. Two different strains of a mutant phage infected a single bacterium. One phage strain is a –b+ and the other is a +b–. The coinfected phages produced the wild-type phenotype in the bacterium: progeny phages were diluted and plated on a bacterial lawn. The resulting plaques produced the following genotypes: 19 a + b+, 31 a –b+, 29 a +b–, 21 a –b–. What is the recombination frequency between the a and b genes?
A) 10%
B) 20%
C) 30%
D) 40%
E) 50%
41. What are plasmids, and what purposes do they serve?
42. In order to better understand arginine biosynthesis in bacteria, a microbial geneticist might first isolate mutant bacterial strains.
a. What characteristics must these mutant bacteria have?
b. Outline a strategy for isolating such mutants.
c. List three possible methods for mapping the genetic location of the mutations in these strains.
43. What causes an F– cell to be converted to F+?
44. What causes an F– cell to be converted to Hfr in the presence of F+ cells?
45. Outline the steps involved in mapping a bacterial chromosome by conjugation.
46. Outline the steps involved in mapping a bacterial chromosome by cotransformation.
47. You perform interrupted conjugation using an a +b+ c +d+l+ m + n + o + Hfr strain and an F–strain that is a –b–c –d–l–m –n –o –. You observe the following genes transferred together in order from last to first.
n + a + c + m+
o + m + c + a + n+ o +b+d+l+ n+
What is the map order of the genes?
48. (a) Explain how chromosomal genes are transferred from donors to recipients when cells of an F+ strain are mixed with F– cells. (b) Explain why transfer of chromosomal genes occurs at a higher frequency when cells of an Hfr strain are mixed with F– cells.
49. (a) What is an F plasmid, and how is it formed? (b) Explain how an F can be used to construct a bacterial strain that is partially diploid. (c) Explain how partial diploid strains can be used to assess interactions between different alleles (e.g., lac+ and lac–).
50. Explain the significance of horizontal gene transfer to bacterial evolution and to our ability to discern relationships between different groups of bacteria.
51. Outline the steps involved in mapping bacterial genes by generalized transduction.
52. How does a virulent phage differ from a temperate phage?
53. Both retroviruses and lysogenic bacteriophages employ a mechanism that allows them to be replicated and passed from cell to cell without producing viruses. What is the common mechanism that these two very different viruses use?
54. A retrovirus has an RNA genome but integrates into the DNA chromosome of a host cell. Explain how it does this.
55. List and describe three different ways that DNA from one bacterium can be transferred into bacterial cells.
56. What is the difference between specialized and generalized transduction?
57. You are using phages to map three toxin-production genes (R, Y, and G) in a new bacterium. You grow phages in a strain of the bacteria that produces all three toxins (R+ , Y+ , G+), isolate the phage, and then infect a second bacterial strain that cannot produce any of the toxins (R–, Y–, G–). The recipient bacteria are then grown on colorimetric media (media that change color in response to toxin presence) to see which toxin genes are transferred together by the phage. The data are as follows:
a. What kind of mapping is this called?
b. Which gene is in the middle?
c. Which of the outside genes is closer to the middle gene?
58. HIV has a high mutation rate. What causes this, and how might this be advantageous to the virus?
59. Two phage phenotypes are controlled by the genes a and b. In a mapping experiment, a culture of bacteria is infected simultaneously with an a –b+ strain and an a +b– strain. When plaques are analyzed, 5 out of 1000 have the a +b+ or a –b– phenotype. Based on the information, how far apart are genes a and b?
60. A virulent bacteriophage is used to infect a prototrophic bacterial culture. Phages are collected from the culture and are used to infect a new bacterial strain that has several auxotrophies. After infection, rare prototrophs are found.
met+ leu+ 0
met+ pro + 1
met+ his+ 0
pro + leu+ 2
pro + his+ 0
leu+ his+ 1
How are the auxotrophy genes organized on the bacterial chromosome?
61. You are studying a new phage that infects H. pylori. You isolated two mutant strains of the phage, each producing a different plaque phenotype due to a specific mutation: rough (r) and big (b). You coinfect H. pylori with both strains by adding a mixture of phages to a culture of cells. You collect the cell lysate containing progeny phages; plate diluted phages on a lawn of H. pylori cells; and observe 970 rough plaques, 890 big plaques, 0 rough and big plaques, and 500 normal, wild-type plaques.
a. What is the recombination frequency between the r locus and the b locus?
b. Can r and b be different alleles of the same locus?
c. How can you explain the results?
62. (a) Explain the mechanism that leads to rapid evolution of the virus that causes influenza. (b) Distinguish between antigenic drift and antigenic shift, and explain the significance of each to influenza evolution and the occurrence of influenza in humans.
Answer Key
1. C 2. E 3. B
C
B 6. B 7. B 8. A 9. C 10. A 11. B 12. A 13. C 14. E
15. D 16. D 17. E
18. A
19. A 20. A
21. E
22. B
23. A
24. C
25. A
26. C
27. B
28. D
29. B
30. B
31. A
32. A
33. D
34. A
35. D
36. B
37. A
38. E
39. A
40. D
41. Plasmids are small, circular, extra-chromosomal DNA molecules found naturally in bacteria. They carry extra genes and can transfer these genes from one bacterial cell to another. They are also used extensively in genetic engineering.