Question

During the analysis of seven \(r I I\) mutations in phage \(\mathrm{T} 4\) mutants \(1,2,\) and 6 were in cistron \(A,\) while mutants \(3,4,\) and 5 were in cistron \(\mathrm{B}\). 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 \((+\text { or }-)\) between 1 and \(2 ; 1\) and \(3 ; 2\) and \(4 ;\) and 4 and 5.

Short answer

Answer: The results of complementation for specific pairs of mutants are as follows: (1) mutants 1 and 2: "-", (2) mutants 1 and 3: "+", (3) mutants 2 and 4: "+", and (4) mutants 4 and 5: "-".

Step-by-step solution

Identify the cistrons of given mutants

We are given the following information about mutants and their cistrons: - Mutants 1, 2, and 6 are in cistron A. - Mutants 3, 4, and 5 are in cistron B. - Mutant 4 is a deletion overlapping mutant 5. - Nothing is known about mutant 7. We will use this information to predict the results of complementation between specific pairs of mutants.

Predict complementation between mutants 1 and 2

Since both mutant 1 and mutant 2 are in cistron A, they will not complement each other. This is because they both have the same functionality, and their deficiencies cannot be compensated for by the other mutant. Therefore, the result of complementation between mutants 1 and 2 is "-".

Predict complementation between mutants 1 and 3

Mutant 1 is in cistron A, while mutant 3 is in cistron B. Since these mutants belong to different cistrons, their different functionalities can complement each other. Therefore, the result of complementation between mutants 1 and 3 is "+".

Predict complementation between mutants 2 and 4

Mutant 2 is in cistron A, while mutant 4 is in cistron B. Similar to the previous step, these two mutants belong to different cistrons, thus their deficiencies in separate functions can be compensated for by the other mutant. Therefore, the result of complementation between mutants 2 and 4 is "+".

Predict complementation between mutants 4 and 5

Both mutant 4 and mutant 5 are in cistron B, and mutant 4 is a deletion overlapping mutant 5. Since both mutants are in the same cistron and have overlapping deletions, they will not complement each other, as they both have defects in the same function. Therefore, the result of complementation between mutants 4 and 5 is "-". In summary, the complementation results are: - Mutants 1 and 2: "-" - Mutants 1 and 3: "+" - Mutants 2 and 4: "+" - Mutants 4 and 5: "-"

Key concepts

Cistron Analysis

Cistron analysis is a crucial aspect of genetic research, helping to identify functional units within a gene. In this process, scientists examine various mutations to determine if they affect the same or different parts of the gene. Each functional unit in a gene is called a cistron, synonymous with the term gene. For phage T4 mutants, such analysis can reveal whether mutations in the same cistron will complement each other or not, which is essentially a test of genetic function. If mutations are in the same cistron, as with mutants 1 and 2 in our exercise, they will not complement as both carry the same defect.

In cases where two mutations affect different cistrons, like mutants 1 and 3, they may provide what the other lacks, allowing them to complement each other. This concept is critical in understanding the genetic makeup and functional regions of phages, as well as other organisms.

Phage T4 Mutants

Phage T4 is a bacteriophage--a type of virus that infects bacteria--which has been extensively studied in molecular genetics. Scientists use phage T4 mutants to understand basic genetic principles. Each mutant carries specific alterations that bring about changes in the phage's genetic information which may result in a loss of function.

As seen with mutant 4 and 5 in the exercise, understanding whether two mutations can complement each other is essential. Given that both are in cistron B with overlapping deletions, their inability to complement each other's function is indicative of their being part of the same genetic block. These studies also have broader implications, allowing researchers to understand how genetic mutations can affect organisms' survival, reproduction, and interaction with their environments.

Point Mutations

Point mutations are simple genetic alterations where a single nucleotide base is changed, inserted, or deleted. These mutations are crucial for understanding genetic diseases and evolution, as they can have significant impacts on protein function.

In mutant 1, 2, and 6 of the exercise, each carries a point mutation within cistron A. Even if these mutants are paired for complementation, they will not rescue each other because they are impaired at the same functional locus. This microscopic change in their genetic code can lead to functional deficiencies. These kinds of mutations are the simplest forms of genetic variation, but their effects can range from harmless to lethal, depending on where they occur and how they alter the genetic code.

Deletion Mutations

Deletion mutations are a form of genetic mutation where a portion of a chromosome or a sequence of DNA is lost during DNA replication. These mutations can be small, affecting only a few nucleotides, or they can be large, involving significant segments of genetic material.

In our example, mutant 4 has a deletion overlapping the region affected in mutant 5. This means that a section of the genetic code is absent in both mutants, a problem that cannot be compensated for by cross-complementation. Deletion mutations like these are critical to observe as they can provide insight into genetic diseases, potential genetic therapies, and biological mechanisms concerning gene expression and regulation.