Concepts of Genetics, 10e (Klug/Cummings/Spencer/Palladino)
Chapter 6 Genetic Analysis and Mapping in Bacteria and Bacteriophages
1) Name two forms of recombination in bacteria.
- A) lytic and lysogenic
- B) auxotrophic and prototrophic
- C) conjugation and transduction
- D) mixed and generalized
- E) insertion and replication
Answer: C
Section: 6.2, 6.5, 6.7
2) Bacteriophages engage in two interactive cycles with bacteria. What are these cycles?
- A) lytic and lysogenic
- B) insertion and replication
- C) auxotrophic and prototrophic
- D) heteroduplex and homoduplex
- E) negative and positive
Answer: A
Section: 6.6
3) A bacteriophage that is capable of entering either a lytic or lysogenic cycle is called a(n) ________.
- A) temperate bacteriophage
- B) virulent bacteriophage
- C) plasmid
- D) episome
- E) plaque-forming unit
Answer: A
Section: 6.6
4) Transduction is a form of recombination in bacteria that involves ________.
- A) 5-bromouracil
- B) F plasmids
- C) bacteriophages
- D) fertility factors
- E) physical contact between the bacteria involved
Answer: C
Section: 6.7
5) The clearing made by bacteriophages in a “lawn” of bacteria on an agar plate is called a ________.
- A) clear zone
- B) lysogenic zone
- C) prophage
- D) plaque.
- E) host range
Answer: D
Section: 6.6
6) Name the general category into which double-stranded circular extrachromosomal DNA elements such as F factors, ColE1, and R would fall.
- A) capsid
- B) r-determinant
- C) plaque
- D) partial diploid
- E) plasmid
Answer: E
Section: 6.4
7) Temperate phages are those that can enter either the ________ or ________ cycle.
- A) lytic; lysogenic
- B) virulent; avirulent
- C) functional; nonfunctional
- D) former; nonformer
- E) complementing; competing
Answer: A
Section: 6.6
8) Lysogeny is an important phenomenon in bacteria and phages. Briefly describe lysogeny (using labeled diagrams if helpful).
Answer: Lysogeny is the process in which a temperate bacteriophage infects a bacterial cell and subsequently integrates its chromosome into the bacterial chromosome.
Section: 6.6
9) Compare and contrast bacteriophage lysis and lysogeny.
Answer: Both lysis and lysogeny involve bacterial/phage interactions related to the production of phage progeny. Lysis occurs when progeny phage burst from the bacterial cell; lysogeny involves the incorporation of the phage chromosome into the bacterial chromosome.
Section: 6.6
10) Jacob, Wollman, and others developed a linkage map of E. coli that is based on time. What form of recombination is involved in generating a linkage map based on time?
Answer: Conjugation: An Hfr bacterium conjugating with an F- strain allows one to generate a map that is dependent on the passage of the donor chromosome across a conjugation tube.
Section: 6.2
11) Assume that the gene trpA in an auxotrophic strain of E. coli is located at 27 minutes, whereas the gene pyrE is located at 81 minutes.
(a) How are minutes arrived at in this context?
(b) Present an experimental scheme that would allow you to convert one of the auxotrophic strains to a prototrophic strain.
Answer:
(a) Minutes are arrived at by a Hfr × F- mating as in the Klug and Cummings text.
(b) Hfr (wild type) × F- (auxotroph)
Section: 6.2
12) Distinguish between F+ and F- bacteria.
Answer: F+ bacteria contain an F factor or plasmid that is capable of initiating conjugation. F- bacteria contain an F plasmid that possess a portion of the bacterial chromosome.
Section: 6.2
13) What is the consequence of a mutation in the recA gene in bacteria?
Answer: The wild-type product of recA is required for bacterial recombination to occur at an appreciable level. Absence of the recA protein diminishes recombination by about 1000-fold.
Section: 6.3
14) How does an auxotroph differ from a prototroph?
Answer: Auxotrophs have lost, through mutation, the ability to grow on minimal medium. Prototrophs are capable of growth on minimal medium.
Section: 6.1
15) Bacteriophages that cannot undergo lysogeny but can infect bacteria are called ________.
Answer: virulent
Section: 6.6
16) Name the term used to describe the phenomenon in which a bacteriophage genome incorporates its genome into the chromosome of the host.
Answer: lysogeny
Section: 6.6
17) When a bacteriophage genome incorporates itself into the chromosome of the host, that phage genome is referred to as a(n) ________.
Answer: prophage
Section: 6.6
18) What is a form of recombination in bacteria that involves the F plasmid?
Answer: conjugation
Section: 6.2
19) What are prototrophs?
Answer: Prototrophs are bacteria that can grow on minimal medium and are assumed to be wild type.
Section: 6.1
20) What is the role of the F factor in bacterial recombination?
Answer: The F factor confers the capacity to produce a conjugation tube, which functions in conjugation by generating the Hfr and F’ recombinant possibilities.
Section: 6.2
21) What is the role of the recBCD genes?
Answer: They function in bacterial recombination.
Section: 6.3
22) Present the general structural features of a plasmid and give an example.
Answer: circular double-stranded DNA existing autonomously in the bacterial cytoplasm; F factor
Section: 6.4
23) What experimental observation demonstrated that genes are involved in the integration of foreign DNA into the bacterial chromosome?
Answer: Mutations allowed identification of rec genes. When such genes were mutated, integration does not occur.
Section: 6.3
24) In general, what two methods are used to grow bacteria in the laboratory?
Answer: liquid and semisolid (agar) media
Section: 6.1
25) Name three forms of recombination in bacteria.
Answer: conjugation, transformation, and transduction
Section: 6.2, 6.5, 6.7
26) Name the typical phases of the bacterial growth cycle in liquid culture medium.
Answer: lag, log (exponential), and stationary
Section: 6.1
27) What is a significant difference between a lytic and a lysogenic cycle?
Answer: In a lytic cycle, the phage genome does not insert into the bacterial chromosome. In the lysogenic cycle, the phage genome inserts into the bacterial chromosome.
Section: 6.6
28) If two different auxotrophic strains are placed in a liquid medium culture tube, prototrophic strains can sometimes be subsequently recovered. Name several mechanisms by which this is possible.
Answer: reverse mutation, genetic suppression, genetic recombination (conjugation, transformation)
Section: 6.2, 6.5, 6.7
29) Describe how different strains of E. coli can reveal different linkage arrangements of genes in Hfr crosses.
Answer: Different strains may have different F factors and therefore different initiation points for chromosome transfer.
Section: 6.2
30) Bacteria that are in a particular physiological state to become transformed are called ________.
Answer: competent
Section: 6.5
31) Explain what is meant by the term heteroduplex in the context of bacterial transformation.
Answer: If transforming DNA is derived from a genetically distinct bacterium, incoming DNA may be different from the host DNA. During initial stages of integration into the bacterial chromosome, the recombinant region contains one strand of DNA that may have a different base sequence than the other strand. Because these strands are not genetically identical (complementary), this double-stranded region is called a heteroduplex.
Section: 6.5
32) Assume that one counted 67 plaques on a bacterial plate where 0.1ml of a 10-5 dilution of phage was added to bacterial culture. What is the initial concentration of the undiluted phage?
Answer: 67 × 105 × 10 = 6.7 × 107 pfu/ml (pfu = plaque-forming units)
Section: 6.6
33) A form of bacterial recombination that involves a viral intermediate is called ________.
Answer: transduction
Section: 6.7
34) What is a bacteriophage?
Answer: A bacteriophage is a virus that has a bacterium as its host.
Section: 6.6
35) What is meant by the term cotransformation?
Answer: Cotransformation occurs when several linked genes are transformed simultaneously.
Section: 6.5
36) Explain the composition and use of minimal medium in the study of bacterial genetics.
Answer: Minimal medium consists of an organic carbon source such as glucose or lactose and a variety of inorganic ions: Na+, K+, Mg++, Ca++ and NH4+. It is useful in isolating bacterial strains (auxotrophs) that are incapable of synthesizing more complex nutritional requirements.
Section: 6.1
37) In what way was the interrupted mating technique used to generate a genetic map in E. coli based on time?
Answer: The interrupted mating technique showed that genes were passed in a linear fashion from the Hfr bacterial strain to an F- strain. By interrupting the mating tube, it could be determined when (in minutes) genes were transferred.
Section: 6.2
38) What is a merozygote?
Answer: A merozygote is a partially diploid cell that results when, through recombination, a portion of a donor chromosome is introduced into a bacterium.
Section: 6.2
39) In a bacterial cross in which the donor (Hfr) is a+b+ and the recipient strain (F-) is a-b-, it is expected that recombinant bacteria will all be a+b+.
Answer: FALSE
Section: 6.2
40) An Hfr cell can initiate chromosome transfer from one E. coli to another.
Answer: TRUE
Section: 6.2
41) To produce recombinants in bacteria, one crossover is better than two.
Answer: FALSE
Section: 6.8
42) R plasmids often contain genes for antibody production.
Answer: FALSE
Section: 6.4
43) A plaque is a substance that causes mutation in bacteria.
Answer: FALSE
Section: 6.6
44) Cotransduction of genes is an indication that the genes are linked.
Answer: TRUE
Section: 6.7
45) Lysogeny is a process that occurs during transformation and conjugation.
Answer: FALSE
Section: 6.6
46) Viral mutations and variants are often categorized by changes in host range and/or plaque morphology.
Answer: TRUE
Section: 6.6
47) A symbiotic relationship between a phage and a bacterium apparently occurs in the process of lysogeny.
Answer: TRUE
Section: 6.6
48) Lysogeny is most likely associated with transduction.
Answer: TRUE
Section: 6.6
49) The “interrupted mating technique” provides a genetic map in Drosophila.
Answer: FALSE
Section: 6.2
