Exam 6: Genetic Analysis and Mapping in Bacteria and Bacteriophages

In five Hfr strains, each of which was used to build a time-of-entry map, the genes entered the recipient cells as follows: Strain 1: S L A C T F Strain 2: N P F T C A Strain 3: T F P N U Y Strain 4: S H Y U N P Strain 5: U N P F T C Which of the following represents a correct compilation of these results?

When F⁺ conjugation occurs successfully, only one copy of the F plasmid single-stranded DNA is transferred. What else must minimally occur?

To map genes of a bacterial strain, conjugation must be interrupted at given times. Suppose you have Hfr cells of genotype a⁺b+c+d+e+str^R and F^- cells of genotype a^-b-c-d-e-str^S and you combine these two cultures in liquid medium in four blenders at time 0. After intervals of 3, 6, 9, and 12 minutes, you turn on successive blenders. The resulting cultures were then plated on medium containing streptomycin. Why?

Bacterial gene transfer is also used in the lab to introduce genes into organisms of different species, genera, phyla, or even kingdoms or domains. A major example is the use of a Ti plasmid of the soil bacterium Agrobacterium tumefaciens to transfer genes into dicotyledonous plants. The bacterium infects the plant root in the soil and transfers some of the Ti plasmid genes (T DNA)into the plant nucleus. Recombination may occur, and T DNA expression is controlled by plant compounds generated in response to wounding and infection. Assuming you have appropriately engineered the Ti plasmid to carry the gene in question, how could you best and most safely test whether your potatoes are now working as a vaccine?

In generalized transduction, a phage introduces a segment of donor DNA into the recipient cell. This is followed by recombination of the donor fragment with the recipient chromosome. Which of the following must occur?

To map genes of a bacterial strain, conjugation must be interrupted at given times. Suppose you have Hfr cells of genotype a⁺b⁺c⁺d⁺e⁺str^R and F^- cells of genotype a^-b^-c^-d^-e^-str^S and you combine these two cultures in liquid medium in four blenders at time 0. After intervals of 3, 6, 9, and 12 minutes, you turn on successive blenders. What role does the blender play in the experiment?

In Hfr transfer, what happens to linear DNA that does not recombine with the host chromosome?

Which, if any, characteristics of bacterial gene transfer is/are useful in analyzing eukaryotic gene transfer?

In a conjugation experiment, the Hfr donor is thr⁺, leu⁺, his⁺, str. The recipient is thr^-, leu^-, his^-, str^S. Why would you use medium containing streptomycin to analyze your results?

Which of the following allows the compilation of time-of-entry maps?

Conjugation, transduction, and transformation all occur in nature. Which do you expect would more likely account for the acquisition of the genes for resistance to an antibiotic? Why? Which do you think would best account for the acquisition of genes from one bacterial species by another of a different genus? Why?

Bacterial gene transfer is also used in the lab to introduce genes into organisms of different species, genera, phyla, or even kingdoms or domains. A major example is the use of a Ti plasmid of the soil bacterium Agrobacterium tumefaciens to transfer genes into dicotyledonous plants. The bacterium infects the plant root in the soil and transfers some of the Ti plasmid genes (T DNA)into the plant nucleus. Recombination may occur, and T DNA expression is controlled by plant compounds generated in response to wounding and infection. The T DNA is generated when there is a nick that creates a primer for replication, followed by transfer of a single-stranded DNA piece that converts to a double-stranded piece in the plant nucleus. Which of these processes is Ti plasmid transfer most like?

To integrate an F plasmid's genes into a host chromosome, there must be DNA recombination at homologous regions on the two circular strands. What is the minimum number of such crossover events needed for integration?

Benzer's analysis of phage genomes included deletion mapping. Since recombination could not occur in the area of a deletion, an infection by two phage strains, one of which has a deletion and the other a point mutation, that results in no wild-type recombinants being produced indicates ________.

Explain when, why, and how recombination in bacteria is like crossing over in diploid cells.

Why does conjugation with an Hfr donor result in a much higher rate of gene transfer than conjugation with an F⁺ donor?

Seymour Benzer's fine structure studies of genomes used mutations found in specific regions of what kind of genome?

In a partially diploid F′ exconjugant, there are two alleles for lac (1 and 2)and two alleles for his (3 and 4). The phenotype of this cell is identical to a lac 1 his 4 cell. What is the best interpretation?

Bacterial gene transfer is also used in the lab to introduce genes into organisms of different species, genera, phyla, or even kingdoms or domains. A major example is the use of a Ti plasmid of the soil bacterium Agrobacterium tumefaciens to transfer genes into dicotyledonous plants. The bacterium infects the plant root in the soil and transfers some of the Ti plasmid genes (T DNA)into the plant nucleus. Recombination may occur, and T DNA expression is controlled by plant compounds generated in response to wounding and infection. This method can be used to introduce a gene for an antigenic protein into an edible plant, such as a potato, to produce an edible vaccine (e.g., for cholera). What has to be made a part of the Ti plasmid?

An F′ donor includes F DNA plus a segment of bacterial chromosome DNA. If conjugation is interrupted before the entire F′ chromosome transfers, what could be the expected consequences?