NEET Molecular Basis of Inheritance PYQs & Practice Questions

10 free NEET Biology questions on Molecular Basis of Inheritance, starting with previous year questions (2016–2026). Tap “Show answer” to check each one. No login needed.

Topics: Classification of DNA and RNA Sugars · Nucleoside vs. Nucleotide · Bonds Linking Nucleotides in DNA · Uniform Width of the DNA Double Helix · Charge on DNA and Histone Proteins · Location of Promoter and Terminator in Transcription · Key Facts About Sickle Cell Anaemia · The Codon AUG · The First Genetic Material · Introns and Exons in Mature mRNA · Gene Density Across Human Chromosomes · Scientists and the DNA Double Helix Model

Q1NEET 2026Lac Operon Regulation
Which of the following statements about lac-operon is correct?
- A. Lactose activates repressor to bind to the operator
- B. Genes i, z, y and a share single common promoter
- C. Galactose can act as an inducer of lac operon
- D. Gene i is constitutively expressed
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Answer: C — Galactose can act as an inducer of lac operon
The regulatory gene 'i' (encoding the lac repressor) is constitutively expressed, i.e., it is always transcribed at a low, constant level, independent of lactose presence. (Lactose/allolactose actually INACTIVATES the repressor, not activates it, to allow transcription; the structural genes z, y, a share a common promoter, but gene i has its own separate promoter.)
Q2NEET 2026RNA Polymerases and Transcription
Which of the following enzymes synthesizes precursor mRNA?
- A. RNA polymerase II
- B. RNA polymerase III
- C. DNA polymerase
- D. RNA polymerase I
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Answer: —
In eukaryotes, RNA polymerase II transcribes precursor mRNA (hnRNA), which is later processed (capping, tailing, splicing) into mature mRNA. RNA polymerase I transcribes rRNA, and RNA polymerase III transcribes tRNA and other small RNAs.
Q3NEET 2026Statements about restriction endonucleases
Which of the following statements are not true regarding restriction endonucleases? A. They are called molecular scissors. B. They are the enzymes responsible for restricting the growth of bacteriophages in E. coli. C. They cut the DNA only at the centre of the palindromic sites. D. They remove nucleotides only from the ends of DNA fragments. E. They recognise specific palindromic base-pair sequences.
- A. C and D only
- B. A and E only
- C. D and E only
- D. A and B only
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Answer: —
A, B, E are true (standard description of restriction enzymes). C is false (they cut near but not necessarily exactly at the centre, and action varies). D is false (restriction enzymes cut internally, not just remove end nucleotides — that's exonuclease action). So C and D only are not true.
Q4NEET 2026lac operon z gene product
In the lac operon, the z gene codes for:
- A. the repressor of lac operon
- B. transacetylase
- C. permease
- D. beta-galactosidase
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Answer: C — permease
The lacZ gene codes for beta-galactosidase, the enzyme that hydrolyses lactose.

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Q5NEET 2026Correct statements about transcription unit
Which of the following statements are correct with reference to a transcription unit in DNA? A. A transcription unit is defined primarily by three regions: promoter, structural gene and terminator. B. The promoter is said to be located towards the 5'-end of the structural gene. C. The promoter is a DNA sequence that provides binding site for RNA polymerase. D. The promoter defines the template and coding strands. E. The terminator is located towards the 3'-end of the coding strand and it defines the end of the process of transcription.
- A. B, C, D and E only
- B. A, B, C and E only
- C. A, B, C, D and E
- D. A, C, D and E only
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Answer: C — A, B, C, D and E
A, B, C, D, E are all standard correct features of a transcription unit — all correct.
Q6NEET 2026Arranging DNA fingerprinting steps
Arrange the following steps of DNA fingerprinting in a correct sequence: A. Isolation of DNA and its digestion by restriction endonucleases. B. Hybridisation using a labelled VNTR probe. C. Transferring of separated DNA fragments to synthetic membranes. D. Detection of hybridised DNA fragments by autoradiography. E. Separation of DNA fragments by electrophoresis.
- A. A, E, B, C, D
- B. A, D, B, E, C
- C. A, B, D, C, E
- D. A, E, C, B, D
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Answer: C — A, B, D, C, E
Sequence: isolate & digest DNA (A) → separate by electrophoresis (E) → transfer to membrane (C) → hybridise with probe (B) → detect by autoradiography (D): A, E, C, B, D.
Q7NEET 2026Correct statements about packaging of DNA helix
Which of the following statements are correct with reference to packaging of DNA helix? A. Histones are organized to form a unit of eight molecules called histone octamer. B. Histones are negatively charged basic proteins. C. Histones are rich in the basic amino acid residues - lysine and arginine. D. The positively charged DNA is wrapped around the histone octamer to form nucleosome. E. The packaging of chromatin at higher levels requires an additional set of proteins called non-histone chromosomal proteins.
- A. B, D and E only
- B. A, B and D only
- C. C, D and E only
- D. A, C and E only
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Answer: C — C, D and E only
A (histone octamer of 8 molecules) is correct; C (rich in lysine/arginine) is correct; E (non-histone chromosomal proteins for higher packaging) is correct. B is false (histones are positively charged, not negatively). D is false (DNA, not histones, is negatively charged and wraps around the octamer). A, C and E only.
Q8NEET 2026Correct sequence of steps in PCR
Identify the correct sequence of steps in each cycle of Polymerase Chain Reaction (PCR):
- A. Denaturation→Extension→Annealing
- B. Denaturation→Annealing→Extension
- C. Annealing→Denaturation→Extension
- D. Extension→Denaturation→Annealing
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Answer: A — Denaturation→Extension→Annealing
PCR cycle: denaturation (DNA strands separate) → annealing (primers bind) → extension (DNA polymerase synthesizes new strand).

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Q9NEET 2026Sixth mutant codon of beta globin gene
The sixth mutant codon of beta globin gene causing polymerization of Haemoglobin and change in RBC shape is ___________.
- A. CAG
- B. AUG
- C. GUG
- D. GAG
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Answer: B — AUG
In sickle-cell anaemia, the sixth codon of the beta-globin gene is mutated from GAG to GUG, causing Glu→Val substitution and haemoglobin polymerization.
Q10NEET 2025Translation and RNA Interference
Given below are two statements : Statement I : Transfer RNAs and ribosomal RNA do not interact with mRNA. Statement II : RNA interference (RNAi) takes place in all eukaryotic organisms as a method of cellular defence. In the light of the above statements, choose the most appropriate answer from the options given below :
- A. Both Statement I and Statement II are correct
- B. Both Statement I and Statement II are incorrect
- C. Statement I is correct but Statement II is incorrect
- D. Statement I is incorrect but Statement II is correct
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Answer: C — Statement I is correct but Statement II is incorrect
Statement I is incorrect: tRNA and rRNA DO interact with mRNA during the translation process. Statement II is correct: RNA interference occurs in all eukaryotic organisms as a method of cellular defence.

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