Q.16 Which of the following mutations is least deleterious in a genome :
1. Missense mutation
2. Non-sense mutation
3. Silent mutation
4. Violent mutations
Silent mutation is the least deleterious type of mutation in a genome because it does not alter the amino acid sequence of the protein. This makes it the correct answer (option 3) in this genetics MCQ, commonly tested in exams like GATE Life Sciences.
Question Breakdown
This question assesses understanding of point mutations’ impacts on protein function and organism fitness, a key topic in molecular genetics.
Option Analysis
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Option 1: Missense mutation
Moderately deleterious. It substitutes one amino acid for another due to a single nucleotide change, potentially disrupting protein structure or function (e.g., sickle cell anemia from valine replacing glutamic acid in hemoglobin). -
Option 2: Non-sense mutation
Highly deleterious. It creates a premature stop codon, truncating the protein and often rendering it non-functional, leading to loss-of-function diseases like cystic fibrosis. -
Option 3: Silent mutation
Least deleterious. It changes a codon but codes for the same amino acid due to genetic code degeneracy (e.g., CUU to CUC both specify leucine), with no impact on protein sequence or typically function. -
Option 4: Violent mutations
Incorrect term; not a standard mutation type. Likely a distractor—genetics recognizes no such category.
Introduction to Deleterious Mutations
Mutations least deleterious in genome are silent mutations, which preserve protein function despite DNA changes. In genetics, mutation impact varies by type, crucial for evolutionary biology and exams testing point mutations’ effects on fitness.
Mutation Types Ranked by Harm
Silent mutations rank least harmful as they don’t change amino acids, unlike missense (alters one amino acid) or nonsense (premature stop). “Violent” isn’t valid—focus on standard classifications like substitutions.
| Mutation Type | Effect on Protein | Deleterious Level | Example |
|---|---|---|---|
| Silent | No amino acid change | Least | GAA to GAG (both glutamic acid) |
| Missense | Single amino acid swap | Moderate | Sickle cell: GAG to GTG |
| Nonsense | Truncated protein | High | Stop codon creation |
| Violent | Non-existent | N/A | Distractor option |
Why Silent Mutations Matter
Due to the degenerate genetic code (64 codons for 20 amino acids), third-position changes often stay silent, enabling neutral evolution without fitness loss. They accumulate fastest in genomes. For exams, remember: silent = synonymous = harmless.
