Ch. 6 - Genetic Analysis and Mapping in Bacteria and Bacteriophages

Klug - Concepts of Genetics 12th Edition

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Klug 12th Edition

Ch. 6 - Genetic Analysis and Mapping in Bacteria and Bacteriophages

Problem 18

Chapter 6, Problem 18

In an analysis of rII mutants, complementation testing yielded the following results:

Verified step by step guidance

Understand the concept of complementation testing: Complementation testing is used to determine whether two mutations are in the same gene or in different genes. If two mutants complement each other (indicated by '+'), it means their mutations are in different genes. If they do not complement (indicated by '-'), their mutations are in the same gene.

Analyze the given data: Mutants 1 and 2 complement (+), meaning their mutations are in different genes. Similarly, mutants 1 and 3 complement (+), so their mutations are also in different genes. However, mutants 1 and 4 do not complement (-), meaning their mutations are in the same gene. The same applies to mutants 1 and 5 (-).

Group the mutants based on the complementation results: Since mutants 1 and 4, as well as mutants 1 and 5, do not complement, mutants 4 and 5 are likely in the same gene as mutant 1. Mutants 2 and 3, which complement mutant 1, are in different genes.

Predict the results for mutants 2 and 3: Since mutants 2 and 3 complement mutant 1 and are in different genes, they are likely to complement each other. The predicted result for 2 and 3 is '+'.

Predict the results for mutants 2 and 4, and 3 and 4: Mutant 4 is in the same gene as mutant 1, while mutants 2 and 3 are in different genes. Therefore, mutants 2 and 4, as well as mutants 3 and 4, are predicted to complement each other. The predicted results for both 2 and 4, and 3 and 4, are '+'.

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Key Concepts

Here are the essential concepts you must grasp in order to answer the question correctly.

Complementation Testing

Complementation testing is a genetic technique used to determine whether two mutations that produce a similar phenotype are in the same gene or in different genes. If two mutants complement each other (show a '+' result), it indicates that they are in different genes, as the wild-type function is restored. Conversely, if they do not complement (show a '-' result), it suggests that the mutations are in the same gene, preventing the restoration of function.

rII Mutants

rII mutants are a class of mutations in the T4 bacteriophage that affect its ability to lyse bacterial cells. These mutants are often used in genetic studies to understand gene function and interactions. The rII region is particularly useful for complementation tests because it contains genes that can exhibit distinct phenotypes when mutated, allowing researchers to analyze genetic relationships and functional redundancy.

Genetic Interaction

Genetic interaction refers to the way in which different genes influence each other's expression and function. In the context of complementation testing, understanding genetic interactions helps predict the outcomes of combining different mutants. For example, if two mutants affect the same pathway or process, their interaction may lead to a specific phenotype, which can be inferred from previous results, guiding predictions about new combinations of mutants.

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Related Practice

Textbook Question

If a single bacteriophage infects one E. coli cell present on a lawn of bacteria and, upon lysis, yields 200 viable viruses, how many phages will exist in a single plaque if three more lytic cycles occur?

In recombination studies of the rII locus in phage T4, what is the significance of the value determined by calculating phage growth in the K12 versus the B strains of E. coli following simultaneous infection in E. coli B? Which value is always greater?

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Textbook Question

If further testing of the mutations in Problem 18 yielded the following results, what would you conclude about mutant 5?

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Textbook Question

Using mutants 2 and 3 from Problem 19, following mixed infection on E. coli B, progeny viruses were plated in a series of dilutions on both E. coli B and K12 with the following results.

What is the recombination frequency between the two mutants?

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Textbook Question

Using mutants 2 and 3 from Problem 19, following mixed infection on E. coli B, progeny viruses were plated in a series of dilutions on both E. coli B and K12 with the following results.

Another mutation, 6, was tested in relation to mutations 1 through 5 from Problems 18–20. In initial testing, mutant 6 complemented mutants 2 and 3. In recombination testing with 1, 4, and 5, mutant 6 yielded recombinants with 1 and 5, but not with 4. What can you conclude about mutation 6?

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