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NEET Molecular Basis of Inheritance: 5 practice MCQs

By the PrepMatic team · Updated 9 Oct 2026 · 3 min read

Molecular Basis of Inheritance explains how DNA stores, copies and expresses genetic information. It is a Class 12 Biology chapter where the classic experiments, the central dogma and gene regulation each produce regular questions. The five MCQs below test the Hershey-Chase experiment, Meselson and Stahl's result, the template strand, the number of sense codons and the lac operon inducer.

What this chapter covers in the NEET syllabus

The NMC unit is Genetics and Evolution, and the molecular genetics half is the Class 12 NCERT chapter Molecular Basis of Inheritance. The topics are:

• The search for the genetic material: Griffith, Avery-MacLeod-McCarty and Hershey-Chase.
• The structure of DNA and RNA, the packaging of DNA, and the double helix.
• DNA replication: the semi-conservative mechanism.
• Transcription, genetic code, translation and the central dogma.
• Regulation of gene expression: the lac operon.
• The Human Genome Project and DNA fingerprinting.

Five practice MCQs on the Molecular Basis of Inheritance

Question 1

In their experiments with bacteriophages, Hershey and Chase labelled the viral DNA with:

• A. ³⁵S
• B. ³²P
• C. ¹⁵N
• D. ¹⁴C

Question 2

E. coli with ¹⁵N-labelled DNA is transferred to ¹⁴N medium and allowed to divide twice. The DNA molecules after two generations are:

• A. 50% hybrid (¹⁵N-¹⁴N) and 50% light (¹⁴N-¹⁴N)
• B. all hybrid
• C. all light
• D. 25% hybrid and 75% light

Question 3

In transcription, the DNA strand that serves as the template for RNA synthesis has the polarity:

• A. 5′ to 3′
• B. 3′ to 5′
• C. alternately 5′ to 3′ and 3′ to 5′
• D. random

Question 4

Out of the 64 codons of the genetic code, the number that code for amino acids is:

• A. 64
• B. 20
• C. 61
• D. 3

Question 5

In the lac operon of E. coli, the inducer is:

• A. glucose
• B. galactose
• C. β-galactosidase
• D. lactose

Answers and explanations

1. B. Hershey and Chase grew one batch of phages with ³²P (which labels DNA, since proteins have no phosphorus) and another with ³⁵S (which labels proteins, since DNA has no sulphur). Only ³²P entered the bacteria, showing that DNA is the genetic material.
2. A. Meselson and Stahl showed semi-conservative replication. After one generation all DNA is hybrid. After the second generation, half the molecules are hybrid and half are light, which matches the semi-conservative model and rules out conservative replication.
3. B. RNA polymerase reads the template strand in the 3′ to 5′ direction and builds the new RNA 5′ to 3′. The other strand, the coding strand, has the same sequence as the RNA, with T in place of U.
4. C. There are 64 codons, of which 61 code for amino acids and 3 (UAA, UAG, UGA) are stop codons. AUG codes for methionine and also acts as the start codon. The 20 amino acids are coded by these 61 codons, so the code is degenerate.
5. D. In the lac operon, the repressor normally binds the operator and blocks transcription. Lactose (as allolactose) acts as the inducer, binding the repressor and allowing the structural genes lac z, y and a to be transcribed. β-galactosidase is the enzyme product of lac z.

How to prepare the Molecular Basis of Inheritance

• Learn the experiments with their one-line conclusions. Griffith (transformation), Avery, MacLeod and McCarty (DNA is the transforming principle), Hershey and Chase (DNA is the genetic material), Meselson and Stahl (semi-conservative replication), Nirenberg and Khorana (genetic code).
• Memorise the features of the genetic code: triplet, degenerate, non-overlapping, unambiguous and nearly universal. Know the start and stop codons.
• Understand each stage in order. Replication (helicase, primase, DNA polymerase, leading and lagging strands, Okazaki fragments, ligase), transcription (promoter, initiation, elongation, termination; processing in eukaryotes: capping, tailing and splicing) and translation (tRNA charging, initiation at AUG, elongation, termination).
• Draw the lac operon in its two states, with and without lactose, and label the regulator gene, promoter, operator and the structural genes.
• Keep the numbers: base pairs per turn (10), the distance between base pairs (0.34 nm), the pitch (3.4 nm), and about 3 × 10⁹ base pairs in the human genome.

Because the topics are linked, make one flow chart of the central dogma and revise it often. The NEET genetics and evolution guide covers common mistakes, and the NEET Biology preparation guide fits this chapter into the plan.

Take a full Molecular Basis of Inheritance test on PrepMatic

Once you can draw the central dogma from memory, take a topic test on PrepMatic (about 15 questions in 30 minutes) and see the score with NEET's negative marking. The free Basic plan includes topic tests, and the practice hub lists the next chapters.

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