12. Mutation in gene ‘X’ leads to lethality in a haploid organjsm. Which one of the following is best suited to analyse the function of gene ‘X’?
(1) Pleiotropic mutants
(2) Temperature sensitive mutants
(3) Recessive mutants
(4) Mutants with low penetrance
Temperature sensitive mutants are the best method to study the function of a lethal gene ‘X’ in haploid organisms, as they allow conditional expression at permissive temperatures while revealing loss-of-function phenotypes at restrictive conditions. In haploid systems like yeast or fungi, null mutations cause immediate death, preventing functional analysis, but temperature-sensitive (ts) variants produce proteins stable at low temperatures (e.g., 25°C) yet unstable at high ones (e.g., 37°C), enabling timing of gene action during development. This approach is standard in genetics for essential genes, as confirmed in CSIR NET questions.
Option Analysis
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Pleiotropic mutants: These affect multiple traits but do not solve lethality in haploids, as the organism dies before phenotypes manifest; they suit diploid studies for multifunctionality, not essential gene timing.
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Temperature sensitive mutants: Ideal choice, as conditional lethality permits growth at permissive temperatures and phenotype observation at restrictive ones, pinpointing gene role without constitutive death.
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Recessive mutants: Irrelevant in haploids, where all mutations express dominantly due to single genome copy; no masking occurs.
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Mutants with low penetrance: These show incomplete expression, but lethality still kills most haploids, failing reliable functional study.
Why Temperature Sensitive Mutants Excel
Ts mutants generate proteins with temperature-dependent stability, often from missense changes affecting folding, allowing shift experiments to map gene function temporally, as in Habrobracon or yeast screens. Unlike other options, they bypass haploid lethality barriers, supporting screens for essential genes via mutagenesis and selection. For CSIR NET aspirants, this distinguishes conditional lethals as key for haploid genetics.
