Section 16 — NEET-Pattern Practice Questions (Molecular Basis of Inheritance)
Molecular Basis of Inheritance is one of the highest-yield NEET chapters in all of Class 12 Biology — it is consistently among the most heavily represented chapters, with multiple questions in most years. The questions span the whole story of the chapter: DNA structure and Chargaff's rule, packaging, the classic experiments (Griffith, Avery, Hershey-Chase, Meselson-Stahl), replication enzymes, transcription, the genetic code, translation, the lac operon, the Human Genome Project and DNA fingerprinting.
This section is a focused 28-question NEET-pattern practice quiz covering the entire chapter — a mix of straight recall (who, what, how many), single-step calculations (Chargaff percentages, hybrid-DNA fractions, codon counts) and concept traps (template vs coding strand, degenerate vs unambiguous, induction in the lac operon).
Important note: These are NEET-pattern practice questions built on the recurring core concepts of this chapter. Do not treat them as exact authenticated year-tagged NEET PYQs unless each one is separately matched against an official NEET paper and year.
How to use: Treat this like a timed mock — give yourself about 25 minutes for all 28 questions. Attempt first, then read each explanation carefully. Use the Mini Memory Capsule below to spot the recurring question patterns before you begin.
Mini Memory Capsule — NEET's Top Hooks for This Chapter
Most NEET questions on Molecular Basis of Inheritance fall into these recurring patterns:
1. Chargaff & DNA structure — A = T, G = C; A=T has 2 H-bonds, G≡C has 3; pitch 3.4 nm, 10 bp/turn, 0.34 nm/bp. Calculate base percentages from one value.
2. Packaging numbers — nucleosome ≈ 200 bp, histone octamer = 8 molecules, DNA length ≈ 2.2 m (6.6 × 10⁹ bp × 0.34 nm).
3. The classic experiments — Griffith (transforming principle), Avery (DNase abolishes transformation), Hershey-Chase (³²P = DNA, ³⁵S = protein), Meselson-Stahl (¹⁵N → ¹⁴N, density gradient, hybrid band after 1 generation).
4. Replication machinery — DNA-dependent DNA polymerase works only 5'→3'; leading vs lagging; Okazaki fragments joined by DNA ligase; origin of replication.
5. Transcription — transcription unit = promoter + structural gene + terminator; template vs coding strand; eukaryotic RNA pol I (rRNA), II (hnRNA/mRNA), III (tRNA, 5S rRNA, snRNA); splicing/capping/tailing.
6. Genetic code — 64 codons, 61 coding, 3 stop (UAA, UAG, UGA), AUG = start + Met; degenerate, unambiguous, nearly universal; tRNA the adapter (Crick).
7. Translation — ribosome is the site; rRNA is the ribozyme that forms the peptide bond; initiation → elongation → termination; UTRs at both ends.
8. Lac operon — z = β-galactosidase, y = permease, a = transacetylase, i = repressor; lactose = inducer; negative regulation (Jacob & Monod).
9. HGP & DNA fingerprinting — HGP 1990–2003, ≈30,000 genes, 99.9% identical, <2% coding, chr1 = 2968 / Y = 231; fingerprinting by Jeffreys, VNTR, Southern blot.