Concept explainers
HOW DO WE KNOW?
In this chapter, we have focused on genetic systems present in bacteria and on the viruses that use bacteria as hosts (bacteriophages). In particular, we discussed mechanisms by which bacteria and their phages undergo genetic recombination, which allows geneticists to map bacterial and bacteriophage chromosomes. In the process, we found many opportunities to consider how this information was acquired. From the explanations given in the chapter, what answers would you propose to the following questions?
- (a) How do we know that genes exist in bacteria and bacteriophages?
- (b) How do we know that bacteria undergo genetic recombination, allowing the transfer of genes from one organism to another?
- (c) How do we know whether or not genetic recombination between bacteria involves cell-to-cell contact?
- (d) How do we know that bacteriophages recombine genetic material through transduction and that cell-to-cell contact is not essential for transduction to occur?
- (e) How do we know that intergenic exchange occurs in bacteriophages?
- (f) How do we know that in bacteriophage T4 the rII locus is subdivided into two regions, or cistrons?
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Chapter 6 Solutions
Concepts of Genetics (11th Edition)
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- Imagine that you are a student in Alfred Hershey and Martha Chase’s lab in the late 1940s. You are given five test tubes containing E. Coli bacteria infected with T2 bacteriophages that have been labeled with either 32P or 35S. Unfortunately, you forget to mark the tubes and are now uncertain about which tubes is which. You performed their blender experiment and got the following results. Which tube out of these 5 contains E. Coli infected with 32P-labeled phage? Explain your answer.arrow_forwardA person with a rare genetic disease has a sample of her chromosomessubjected to in situ hybridization using a probe that is known to recognize band p11 on chromosome 7. Even though her chromosomes look cytologically normal, the probe does not bind to this person’s chromosomes. How would you explain these results? How would you use this information to positionally clone the gene that is related to this disease?arrow_forwardIn the Hershey Chase experiment, why was the localization of radio-labeled phage of macromolecules in the cytoplasm the reason that the genetic material identity was proved.arrow_forward
- A group of genetics students mix two auxotrophic strains of bacteria: one is leu+ trp+ his− met− and the other is leu− trp− his+ met+. After mixing the two strains, they plate the bacteria on minimal medium and observe a few prototrophic colonies (leu+ trp+ his+ met+). They assume that some gene transfer has taken place between the two strains. How can they determine whether the transfer of genes is due to conjugation, transduction, or transformation?arrow_forwardWhat is horizontal gene transfer? What are the three mechanisms for this to occur in bacteria? What are the components needed for the processes of transformation, conjugation, and transduction? How does each process occur? What genes are involved in each process? How do generalized and specialized transduction differ? What is the end result of each? What is recombination? What is the importance to bacteria & archaea? What are the two types of recombination? What are the details of each type? What components are needed for each type?arrow_forwardFor bacteria living in a rapidly changing environment, would a population of bacteria capable of conjugation be more successful than one that could not undergo conjugation? Explain why. Include in your answer a description of the process of conjugation and its advantages over other mechanisms of DNA transfer between prokaryotic organisms.arrow_forward
- Austin Taylor and Edward Adelberg isolated some new strains of Hfr cells that they then used to map several genes in E. coli by using interrupted conjugation . In one experiment, they mixed cells of Hfr strain AB-312, which were xyl+ mtl+ mal+ met+ and sensitive to phage T6, with F− strain AB-531, which was xyl− mtl− mal− met− and resistant to phage T6. The cells were allowed to undergo conjugation. At regular intervals, the researchers removed a sample of cells and interrupted conjugation by killing the Hfr cells with phage T6. The F− cells, which were resistant to phage T6, survivedand were then tested for the presence of genes transferred from the Hfr strain. The results of this experiment are shown in the accompanying graph. On the basis of these data, give the order of the xyl, mtl, mal, and met genes on the bacterial chromosome and indicate the minimum distances between them.arrow_forwardBy conducting conjugation experiments between Hfr and recipientstrains, Wollman and Jacob mapped the order of many bacterialgenes. Throughout the course of their studies, they identified severaldifferent Hfr strains in which the F-factor DNA had been integratedat different places along the bacterial chromosome. A sample of theirexperimental results is shown in the table:Draw a map that shows the order of genes and the locations ofthe origins of transfer among these different Hfr strains?arrow_forwardDiscuss how scientists employ a bacteriophagesite-specific recombination system to generateknockin micearrow_forward
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