Determine the correctness or otherwise of the following Assertion [a] and the Reason [r].
Assertion [a]: Chromosome mutations can change the structure of chromosomes.
Reason [r]: All chromosome mutations arise due to nondisjunction of chromosomes during mitosis or meiosis.
Analyzing Assertion [a]: Chromosome Mutations and Structure
The Assertion [a] states that chromosome mutations can change the structure of chromosomes. This is accurate. Chromosome mutations, also known as chromosomal aberrations, encompass changes in chromosome structure, such as deletions, duplications, inversions, and translocations. Therefore, Assertion [a] is true.
Analyzing Reason [r]: Nondisjunction and Mutation Origin
The Reason [r] claims that all chromosome mutations arise due to nondisjunction during mitosis or meiosis. This statement is incorrect.
- Nondisjunction is an error in cell division that results in the incorrect distribution of chromosomes, leading to aneuploidy (abnormal chromosome numbers).
- Structural chromosome mutations (changes in chromosome structure) arise from chromosome breakage and subsequent rearrangement. Causes include spontaneous events, mutagens, or errors during DNA repair, not solely nondisjunction.
Since nondisjunction primarily affects chromosome number and does not account for all types of structural changes, Reason [r] is false.
Conclusion
Based on the analysis, Assertion [a] is true, and Reason [r] is false. This corresponds to Option B.
Important Questions from Mutations and Mutagenesis
A DNA sequence, 5'-ATGGACGTGCTTCCCAAAGCATCGGGC-3', is mutated to obtain
P. 5'-ATGGACGTGCTTCaCAAAGCATCGGGC-3′
Q. 5′-ATGGACGTGCTTCCCgAAAGCATCGGGC-3′
R. 5'-ATGGACGTGCTTCC-AAAGCATCGGGC-3′
S. 5'-ATGGACGTGCTTCCCAAtGCATCGGGC-3′
T. 5'-ATGGACGaGCTTCCCAAAGCATCGGGC-3′
[Point mutations are shown in the lower case or ‘–' within the sequences]
Which of the above mutant sequences DO NOT have frame-shift?
- A mutation in a gene that codes for a polypeptide results in a variant polypeptide that lacks the last three amino acids. What type of mutation is this?
- A truncated polypeptide is synthesized due to a nonsense mutation. Where would you introduce another mutation to obtain a full-length polypeptide?
Determine the correctness or otherwise of the following Assertion (a) and the Reason (r).
Assertion : N-methyl-N'-nitro-N-nitrosoguanidine (NTG) is an effective chemical mutagen.
Reason: Mutations induced by NTG mainly are the GC $\rightarrow$ AT transitions.
- Lysine is being produced in a lab-scale reactor by a threonine auxotroph. After 2 weeks of operation it was observed that the concentration of lysine in the reactor was gradually decreasing. Microbiological assays of reactor samples showed absence of contamination and recorded data showed no change in the operating conditions. The most probable reason for decrease in lysine concentration may be attributed to
