During the analysis of seven rII mutations in phage T4, mutants 1, 2, and 6 were in cistron A, while mutants 3, 4, and 5 were in cistron B. Of these, mutant 4 was a deletion overlapping mutant 5. The remainder were point mutations. Nothing was known about mutant 7. Predict the results of complementation (+ or -) between 1 and 2; 1 and 3; 2 and 4; and 4 and 5.

Verified step by step guidance

1. Understand the concept of complementation: Complementation occurs when two mutations in different cistrons (functional units of a gene) allow the organism to produce a functional product. If the mutations are in the same cistron, complementation does not occur (-). If they are in different cistrons, complementation occurs (+).
2. Identify the cistrons for each mutant: Mutants 1, 2, and 6 are in cistron A, while mutants 3, 4, and 5 are in cistron B. Mutant 7's cistron is unknown. Mutant 4 is a deletion overlapping mutant 5, while the others are point mutations.
3. Analyze the complementation between mutants 1 and 2: Since both mutants 1 and 2 are in cistron A, they cannot complement each other. The result will be (-).
4. Analyze the complementation between mutants 1 and 3: Mutant 1 is in cistron A, and mutant 3 is in cistron B. Since they are in different cistrons, they can complement each other. The result will be (+).
5. Analyze the complementation between mutants 2 and 4, and between mutants 4 and 5: Mutant 2 is in cistron A, and mutant 4 is in cistron B, so they can complement each other (+). However, mutant 4 is a deletion overlapping mutant 5, so they cannot complement each other (-).

Key Concepts

Cistron and Complementation

A cistron is a segment of DNA that encodes a single polypeptide and is synonymous with a gene. Complementation occurs when two different mutations in the same gene are present in a diploid organism, and the wild-type phenotype is restored. In the context of phage T4, if two mutations are in different cistrons, they will complement each other, resulting in a positive complementation test.

Point Mutations vs. Deletions

Point mutations are changes in a single nucleotide base pair in the DNA sequence, which can lead to a change in a single amino acid in a protein. Deletions, on the other hand, involve the loss of a segment of DNA, which can disrupt the reading frame and potentially result in a nonfunctional protein. Understanding the nature of these mutations is crucial for predicting complementation outcomes.

Mutant Analysis in Phage Genetics

In phage genetics, analyzing mutants helps to determine the functional relationships between genes. By studying how different mutations interact, researchers can infer whether they affect the same or different cistrons. This analysis is essential for predicting complementation results, as it reveals whether the mutations can compensate for each other’s effects on the phage's ability to infect host cells.