Q.25 Arrange according to their lower to higher genome size:
- Lambda (λ)
- T4
- ΦX174
- T7
Choose the correct answer:
- (A), (B), (C), (D)
- (B), (A), (C), (D)
- (C), (D), (A), (B)
- (C), (B), (D), (A)
ΦX174 (C: ~5.4 kb) < T7 (D: ~40 kb) < Lambda (A: ~48.5 kb) < T4 (B: ~169 kb). Correct answer: option 3 (C, D, A, B).
Genome Sizes Confirmed
These bacteriophages represent classic model systems in molecular biology with well-characterized genomes:
Phage Code Genome Size Type ΦX174 C 5,386 bp ssDNA, circular T7 D 39,937 bp dsDNA, linear Lambda (λ) A 48,502 bp dsDNA, linear T4 B 168,903 bp dsDNA, linear Option Analysis
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(A) A,B,C,D: Lambda (3rd) before T4 (largest)—wrong order.
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(B) B,A,C,D: T4 (largest) first—completely reversed.
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(C) C,D,A,B: Correct: 5 kb → 40 kb → 48 kb → 169 kb
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(D) C,B,D,A: Places massive T4 (169 kb) before T7 (40 kb)—wrong.
Bacteriophage Genome Size Order: ΦX174 T7 Lambda T4 Arranged
Arrange according to their lower to higher genome size: ΦX174 < T7 < Lambda < T4 represents the definitive order for these bacteriophage genomes (5.4 kb → 40 kb → 48.5 kb → 169 kb). This bacteriophage genome size hierarchy is essential GATE Life Sciences knowledge for virology and sequencing questions.
Why This Order Matters
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ΦX174: Smallest ssDNA phage; first fully sequenced (1977), Illumina control.
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T7: RNA polymerase model; fast replication for expression vectors.
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Lambda: Cloning workhorse; lysogeny/replication model.
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T4: Largest; complex head/tail morphogenesis; infection model.
Visualization
textGenome Size Spectrum:
ΦX174 [====] 5 kb
T7 [================] 40 kb
Lambda [====================] 48 kb
T4 [===================================================================] 169 kb
Exam Strategy
Mnemonic: “Xtra Small Tasty Lamb T-bone” (ΦX174, T7, Lambda, T4). Remember kb orders: 5-40-50-170 (approximate). Distinguish: ssDNA (ΦX174) vs dsDNA (others). PYQs test both absolute sizes and relative ordering.
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