Q.69 Which ONE of the following mutants is used to carry out genetic analysis to determine the function
of an essential gene?
(A) Knock out mutant (B) Deletion mutant
(C) Insertion mutant (D) Temperature sensitive mutant
Temperature sensitive mutant is used to analyze essential gene function.
Question Breakdown
Essential genes are required for viability under normal conditions. Complete loss-of-function mutations (knockouts) are lethal, preventing phenotypic analysis. Temperature sensitive (ts) mutants allow conditional function: normal growth at permissive temperature (25-30°C), loss-of-function at restrictive temperature (37-42°C).
Option Analysis
(A) Knock out mutant
Lethal for essential genes. No viable cells to analyze gene function.
(B) Deletion mutant
Lethal. Complete gene removal prevents growth/survival.
(C) Insertion mutant
Lethal if disrupts essential gene ORF. No colonies form.
(D) Temperature sensitive mutant
Correct. ts alleles (missense mutations) produce functional protein at permissive temperature (25°C), defective protein at restrictive temperature (42°C). Shift experiments reveal essential gene phenotypes.
Correct Choice
(D) Temperature sensitive mutant
Mutants genetic analysis essential gene function uses temperature sensitive conditional lethals, as complete knockouts are inviable.
ts Mutant Mechanism
25°C (permissive): ts protein functional → normal growth
↑ Temperature shift
42°C (restrictive): ts protein misfolds/aggregates → essential function lost
↓ Phenotype analysis (cell cycle arrest, morphology)
Classic examples:
-
dnaAts: DNA replication initiation failure
-
cdc28ts (yeast): Cell cycle G1/S arrest
-
sec61ts: ER protein translocation block
Mutant Comparison
| Mutant Type | Viable for Essential Genes? | Function Analysis? |
|---|---|---|
| (A) Knockout | No (lethal) | No |
| (B) Deletion | No (lethal) | No |
| (C) Insertion | No (lethal) | No |
| (D) ts mutant | Yes (conditional) | Yes |
GATE Exam Relevance
Genetics PYQ tests conditional lethal analysis. Key: ts > amber/suppressor > cold-sensitive. Essential gene screens use ts libraries (UCLA haploid CRISPR, yeast ts collections). Modern: AID-degron (auxin-inducible degradation).
