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Exam 9: Bacterial and Viral Genetic Systems

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Question 21

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You cross an Hfr strain of ala⁺ his^- val⁺ genotype with an F^- strain of ala^- his⁺ val^- genotype and wish to recover F^- ala⁺ his⁺val^- recombinants. Which of the following media should you use that will allow the recombinants to grow and form colonies but not allow growth of the two parental strains?

A) Minimal Moderate with histidine and valine but no alanine
B) Minimal Moderate with valine but no alanine or histidine
C) Minimal Moderate with histidine and alanine but no valine
D) Minimal Moderate with no histidine, alanine, or valine
E) Minimal Moderate with alanine but no histidine or valine

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Question 22

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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 higher risk of giving rise to bacteria with 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 gene to genetically unrelated bacteria.

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Question 23

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The process of transferring DNA from one bacterium to another through a bacteriophage is called:

Which of the following statements about retroviruses is FALSE?

Integrated, inactive phage DNA is called a:

HIV belongs to a group of viruses called _____ viruses.

Which of the following statements about nutritional requirements and growth of bacteria is NOT true?

How are Hfr strains of bacteria different from F⁺ strains?

The transfer of DNA from a donor cell to a recipient cell through a cytoplasmic connection is called:

In a transformation experiment in the bacterium Streptococcus, the donor has the genotype d⁺e⁺f⁺ (order is not known) . The recipient strain is d^-e^-f^- and f⁺ transformants are selected for. The complete genotype is determined for each of the f⁺ transformants and the results are shown below. What is the cotransformation frequency between f and e? $\begin{array} { l c } Genotype&Number~ of ~transformants\\\\a ^ { + } e ^ { + } f ^ { + } & 25 \\ a ^ { + } e ^ { - f ^ { + } } & 4 \\ a ^ { - } e ^ { + } f ^ { + } & 80 \\ a ^ { - } e ^ { - } f ^ { + } & 256 \end{array}$

Which of the following horizontal gene transfer mechanisms specifically uses time as a basic unit of mapping?

What causes an F^- cell to be converted to Hfr in the presence of F⁺ cells?

A wild-type strain (h⁺r⁺) of phage T2 was mixed with a double mutant (hr) for host range (h) and rapid lysis (r) and used with a high multiplicity of infection to infect E. coli B. The progeny from the cross were titered (counted) on a mixture of E. coli B and E. coli B/2 strains. The following plaques were scored: hr,212; h⁺r,114; hr⁺,106; h⁺r⁺,188 What is the approximate recombination frequency for these two loci?

Which of the following statements about bacterial genome is NOT true?

Which type of transduction is used to map distances between phage genes?

A retrovirus has an RNA genome but integrates into the DNA chromosome of a host cell. Explain how it does this.

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 MOST likely to be observed?

A transformation experiment is performed with a donor strain that is resistant to four drugs: A, B, C, and D determined by genes A, B, C, and D. The recipient strain is sensitive to all four drugs. The treated recipient-cell population is divided up and plated on media containing various combinations of the drugs. A cell that is resistant to the added drug(s) will form a colony. The table below shows the results. $\begin{array} { l l l l } \text { Drug(s) Added } & \text { Number of Colonies } & \text { Drug(s) Added } & \text { Number of Colonies } \\\hline \text { None } & 10,000 & \mathrm { BC } & 51 \\\text { A } & 1,156 & \mathrm { BD } & 49 \\\text { B } & 1,148 & \mathrm { CD } & 786 \\\text { C } & 1,161 & \mathrm { ABC } & 30 \\\text { D } & 1,139 & \mathrm { ABD } & 42 \\\text { AB } & 46 & \mathrm { ACD } & 630 \\\text { AC } & 640 & \mathrm { BCD } & 36 \\\text { AD } & 942 & \text { ABCD } & 30\end{array}$ One of the genes is quite distant from the other three that are tightly linked. Which gene is distant from the other three?

Some retroviruses contain genes that can stimulate cell division and cause tumors in host cells. Such genes are called:

Two mutations that affect plaque morphology in a particular phage (a^- and b^-) have been isolated. Phages carrying both mutations (a^-b^-) are mixed with wild-type phage (a⁺b⁺) and added to a culture of bacterial cells. Following infection and lysis, samples of the phage lysate are collected and cultured on bacterial cells. The following numbers of plaques are observed: $\begin{array}{l}\begin{array} { l r } \text { Plaque Phenotype}&{ Number }\\a ^ { + } b ^ { + } & 2043 \\a ^ { + } b & 320 \\a ^ { - } b ^ { + } & 357 \\a^- b ^ { - } & 2134\end{array}\end{array}$ What is the frequency of recombination between the a and b genes?