Molecular Basis of Inheritance – Daily Practice Problem (DPP)

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🎯 NEET 2026 Daily Practice Problem (DPP)

Class 12 | Unit 2: Genetics | Topic: Molecular Basis of Inheritance

Q1. In a double-stranded DNA, the two strands are held together by:

  1. Peptide bonds
  2. Phosphodiester bonds
  3. Hydrogen bonds
  4. Ionic bonds
✅ View Answer & Explanation

Correct Answer: (3) Hydrogen bonds
Explanation: The two strands of DNA are complementary and held together by hydrogen bonds between nitrogenous bases (Adenine pairs with Thymine via 2 H-bonds, Guanine with Cytosine via 3 H-bonds).

Q2. Histones are rich in the basic amino acid residues:

  1. Lysine and Arginine
  2. Aspartic acid and Glutamic acid
  3. Lysine and Proline
  4. Serine and Histidine
✅ View Answer & Explanation

Correct Answer: (1) Lysine and Arginine
Explanation: Histones are positively charged basic proteins organized to form a unit called an octamer. They are rich in basic amino acids lysines and arginines.

[Image of nucleosome structure showing DNA wrapping around histone octamer]

Q3. The unequivocal proof that DNA is the genetic material came from the experiments of:

  1. Frederick Griffith
  2. Avery, MacLeod and McCarty
  3. Hershey and Chase
  4. Watson and Crick
✅ View Answer & Explanation

Correct Answer: (3) Hershey and Chase
Explanation: Alfred Hershey and Martha Chase (1952) worked with bacteriophages and used radioactive phosphorus ($P^{32}$) and sulfur ($S^{35}$) to prove DNA is the genetic material.

Q4. Which enzyme is responsible for the unwinding of the DNA double helix during replication?

  1. DNA Polymerase
  2. Helicase
  3. Ligase
  4. Primase
✅ View Answer & Explanation

Correct Answer: (2) Helicase
Explanation: Helicase unzips the two strands of DNA by breaking hydrogen bonds. DNA Polymerase synthesizes the new strand, and Ligase joins fragments.

Q5. The direction of replication in the leading strand is:

  1. 5′ → 3′
  2. 3′ → 5′
  3. Both directions
  4. Variable
✅ View Answer & Explanation

Correct Answer: (1) 5′ → 3′
Explanation: DNA-dependent DNA polymerase catalyses polymerisation only in one direction, that is 5′ → 3′. The leading strand is synthesized continuously.

Q6. Meselson and Stahl used which isotope to prove semi-conservative DNA replication?

  1. $^{14}C$
  2. $^{15}N$
  3. $^{32}P$
  4. $^{35}S$
✅ View Answer & Explanation

Correct Answer: (2) $^{15}N$
Explanation: They used $^{15}N$ (heavy nitrogen), which is a stable isotope (not radioactive), to distinguish between old and new DNA strands using density gradient centrifugation.

Q7. The coding sequences or expressed sequences in a eukaryotic gene are called:

  1. Introns
  2. Exons
  3. Cistrons
  4. Mutons
✅ View Answer & Explanation

Correct Answer: (2) Exons
Explanation: Exons are the coding sequences that appear in mature or processed RNA. Introns are intervening non-coding sequences removed during splicing.

Q8. The enzyme required for the transcription of mRNA in eukaryotes is:

  1. RNA Polymerase I
  2. RNA Polymerase II
  3. RNA Polymerase III
  4. DNA Polymerase
✅ View Answer & Explanation

Correct Answer: (2) RNA Polymerase II
Explanation: RNA Pol II transcribes the precursor of mRNA (hnRNA). RNA Pol I transcribes rRNAs, and RNA Pol III transcribes tRNA.

Q9. Which one of the following is the ‘Start Codon’?

  1. UAA
  2. UAG
  3. AUG
  4. UGA
✅ View Answer & Explanation

Correct Answer: (3) AUG
Explanation: AUG has dual functions: it codes for Methionine and acts as the start codon. UAA, UAG, and UGA are stop codons.

Q10. In the Lac Operon, the ‘z’ gene codes for:

  1. Permease
  2. Transacetylase
  3. Beta-galactosidase
  4. Repressor protein
✅ View Answer & Explanation

Correct Answer: (3) Beta-galactosidase
Explanation: ‘z’ gene codes for beta-galactosidase (hydrolyzes lactose), ‘y’ gene codes for permease (increases permeability), and ‘a’ gene for transacetylase.

[Image of Lac operon diagram showing regulator and structural genes]

Q11. DNA fingerprinting involves identifying differences in some specific regions in DNA sequence called:

  1. Repetitive DNA
  2. Coding DNA
  3. Non-repetitive DNA
  4. Exons
✅ View Answer & Explanation

Correct Answer: (1) Repetitive DNA
Explanation: A small stretch of DNA is repeated many times (Satellite DNA). These show high degrees of polymorphism and form the basis of DNA fingerprinting.

Q12. Which of the following rRNA acts as a structural RNA as well as a ribozyme in bacteria?

  1. 5S rRNA
  2. 18S rRNA
  3. 23S rRNA
  4. 28S rRNA
✅ View Answer & Explanation

Correct Answer: (3) 23S rRNA
Explanation: The 23S rRNA in prokaryotes acts as a ribozyme (an enzyme made of RNA) facilitating peptide bond formation.

Q13. In the Human Genome Project, the method involving sequencing the whole set of genome containing all the coding and non-coding sequences is called:

  1. Expressed Sequence Tags (ESTs)
  2. Sequence Annotation
  3. Bioinformatics
  4. PCR
✅ View Answer & Explanation

Correct Answer: (2) Sequence Annotation
Explanation: ESTs focus only on coding genes. Sequence Annotation involves sequencing the whole genome and then assigning functions to different regions.

Q14. The adapter molecule that picks up amino acids and takes them to the ribosome is:

  1. mRNA
  2. rRNA
  3. tRNA
  4. hnRNA
✅ View Answer & Explanation

Correct Answer: (3) tRNA
Explanation: tRNA (Transfer RNA) has an anticodon loop to read the genetic code and an amino acid acceptor end.

Q15. Splicing represents the dominance of the:

  1. DNA world
  2. RNA world
  3. Protein world
  4. Microbial world
✅ View Answer & Explanation

Correct Answer: (2) RNA world
Explanation: The presence of introns and the process of removal (splicing) is reminiscent of antiquity and the RNA world.

Q16. During translation, the first phase is:

  1. Binding of mRNA to ribosome
  2. Activation of amino acids
  3. Elongation of polypeptide
  4. Termination
✅ View Answer & Explanation

Correct Answer: (2) Activation of amino acids
Explanation: Amino acids are activated in the presence of ATP and linked to their cognate tRNA (charging of tRNA) before translation begins.

Q17. The repressor of the Lac operon is synthesized constitutively by the:

  1. p gene
  2. i gene
  3. z gene
  4. o gene
✅ View Answer & Explanation

Correct Answer: (2) i gene
Explanation: The ‘i’ gene codes for the Repressor of the lac operon. It is called the regulatory gene.

Q18. The Human Genome Project was launched in the year:

  1. 1980
  2. 1990
  3. 2000
  4. 2003
✅ View Answer & Explanation

Correct Answer: (2) 1990
Explanation: HGP was a 13-year project coordinated by the U.S. Department of Energy and the National Institute of Health, launched in 1990.

Q19. Southern Blotting technique uses which of the following for hybridization?

  1. Radiolabelled DNA probe
  2. Radiolabelled RNA probe
  3. Radiolabelled Protein probe
  4. Antibodies
✅ View Answer & Explanation

Correct Answer: (1) Radiolabelled DNA probe
Explanation: Southern blotting uses radiolabelled VNTR (DNA) probes to hybridize with complementary DNA fragments.

Q20. Which of the following is correct regarding the genetic code?

  1. The code is ambiguous and specific
  2. The code is degenerate
  3. The code is overlapping
  4. The code is punctuated
✅ View Answer & Explanation

Correct Answer: (2) The code is degenerate
Explanation: Some amino acids are coded by more than one codon (degeneracy). The code is unambiguous, non-overlapping, and comma-less.

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