Molecular basis of inheritance MCQ – 38 Most Expected Questions

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Dominate the Biology board paper by mastering the Molecular basis of inheritance MCQ. This curated mock test covers the 38 most critical questions frequently asked in the NCERT Class 12 Biology Exam. These questions are handpicked to build conceptual clarity and speed for your upcoming examination.
Molecular basis of inheritance MCQ – 38 Most Expected Questions

Why This Test -Molecular basis of inheritance MCQ- Matters?


Exam Weightage: For the NCERT Class 12 Biology Exam, this unit carries significant weightage (approx. 18-20 marks combined with Genetics), making it crucial for a high aggregate score. Questions from this chapter often appear as 5-mark case studies or direct competency-based MCQs.
Difficulty: Moderate to Hard (Concept Intensive).

Practice Questions (Live Mock Test) – Molecular basis of inheritance MCQ

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Molecular basis of inheritance MCQ – 38 Most Expected Questions (34 MCQs Test)

Q 1 / 34
In a DNA molecule, the phosphate group is linked to the sugar moiety of the same nucleoside by a specific bond. What is this bond called?
A Glycosidic bond
B Phosphodiester bond
C Ester bond (Phosphoester bond)
D Hydrogen bond
Scenario: A scientist calculates the length of DNA in a typical mammalian cell.
Given: Total base pairs equals 6.6 billion. Distance between two consecutive base pairs equals 0.34 nanometers.
What is the approximate length of this DNA double helix?
A 2.0 meters
B 2.2 meters
C 2.5 meters
D 2.7 meters
Scenario: Analysis of a sea urchin double-stranded DNA sample reveals that 17 percent of the bases are Cytosine.
Based on Chargaff’s rules, what is the percentage of Adenine in this sample?
A 17 percent
B 33 percent
C 34 percent
D 50 percent
Consider the following statements regarding Chromatin:
Assertion (A): Heterochromatin is transcriptionally inactive.
Reason (R): It is densely packed and stains dark.
A Both A and R are true, and R explains A
B Both A and R are true, but R does not explain A
C A is true, but R is false
D A is false, but R is true
Which of the following statements is INCORRECT regarding the experimental proof for semiconservative replication?
A It was first shown in the bacterium Escherichia coli.
B It used heavy Nitrogen-15 to label the DNA.
C It was conducted by Watson and Crick.
D Separation was achieved using Cesium Chloride density gradient centrifugation.
Taylor conducted experiments to prove the semiconservative mode of chromosome replication. Which specific organism did he use for this study?
A Vinca rosea
B Vicia faba (Faba beans)
C Drosophila melanogaster
D E. coli
Which of the following experiments provided the “unequivocal” or final proof that DNA is the genetic material?
A Transformation experiments by Griffith.
B Biochemical characterization by Avery, MacLeod, and McCarty.
C Transduction experiments by Hershey and Chase.
D X-ray diffraction by Franklin and Wilkins.
Consider the following statements regarding DNA Replication:
Assertion (A): The lagging strand is synthesized discontinuously.
Reason (R): DNA polymerase can only polymerize nucleotides in the 5-prime to 3-prime direction.
A Both A and R are true, and R explains A
B Both A and R are true, but R does not explain A
C A is true, but R is false
D A is false, but R is true
Name the specific enzyme responsible for breaking the hydrogen bonds and opening the DNA helix during replication.
A DNA Ligase
B DNA Helicase
C DNA Polymerase
D Primase
Which of the following statements regarding DNA replication is INCORRECT?
A Deoxyribonucleoside triphosphates serve as substrates.
B Deoxyribonucleoside triphosphates provide energy for polymerization.
C The direction of replication is 3-prime to 5-prime.
D It occurs in the S-phase of the cell cycle.
In Eukaryotes, RNA Polymerase 1 is responsible for transcribing which of the following?
A mRNA
B tRNA and snRNA
C rRNAs (28S, 18S, and 5.8S)
D All types of RNA
Which of the following codons serves a dual function as the Starter Codon and also codes for Methionine?
A UAA
B UAG
C AUG
D UGA
Consider the following statements:
Assertion (A): Bacteria (Prokaryotes) do not require spliceosomes.
Reason (R): Bacterial genes are not “split genes”; they lack introns.
A Both A and R are true, and R explains A
B Both A and R are true, but R does not explain A
C A is true, but R is false
D A is false, but R is true
The segment of DNA that is equivalent to a “structural gene” is technically referred to as a:
A Muton
B Cistron
C Operon
D Recon
In E. coli, the RNA polymerase holoenzyme requires a transient factor for the Initiation of transcription. What is this factor?
A Rho factor
B Sigma factor
C Alpha factor
D Delta factor
Which of the following features is NOT applicable to RNA?
A Presence of heterocyclic nitrogenous bases.
B Compliance with Chargaff’s Rule (A equals T, G equals C).
C Complementary base pairing during transcription.
D Presence of 5-prime phosphoryl and 3-prime hydroxyl ends.
In Eukaryotic transcription, the primary transcript (hnRNA) contains both exons and introns. The process of removing introns and joining exons in a defined order is technically called:
A Looping
B Capping
C Slicing
D Splicing
Identify the correct chronological first step in the process of Translation:
A Binding of mRNA to the small subunit of the ribosome.
B Recognition of the DNA molecule.
C Aminoacylation of tRNA (Charging).
D Formation of peptide bond.
Scenario: In an E. coli culture, a nonsense mutation occurs specifically in the lac Y gene of the Lac Operon.
If Lactose is added to the medium, which enzymes will be produced?
A Transacetylase only.
B Beta-galactosidase only.
C Lactose permease and Transacetylase.
D None of the enzymes.
In Gel Electrophoresis, DNA fragments are separated based on their movement through an agarose matrix. Which of the following principles dictates this movement?
A Positively charged fragments move to the farther end.
B Negatively charged fragments remain stationary.
C The smaller the fragment size, the farther it moves.
D The larger the fragment size, the farther it moves.
A specific structure is formed when multiple ribosomes associate with a single mRNA strand to translate it simultaneously. What is this structure called?
A Polysome (or Polyribosome)
B Polyhedral body
C Plastidome
D Nucleosome
Match the Lac Operon gene with its correct product:
(a) i-gene matches (iii) Repressor
(b) z-gene matches (i) Beta-galactosidase
(c) a-gene matches (iv) Transacetylase
(d) y-gene matches (ii) Permease
Which option matches the above pairs?
A (a)-(iii), (b)-(i), (c)-(iv), (d)-(ii)
B (a)-(iii), (b)-(i), (c)-(ii), (d)-(iv)
C (a)-(i), (b)-(iii), (c)-(ii), (d)-(iv)
D (a)-(iii), (b)-(iv), (c)-(i), (d)-(ii)
Which of the following is NOT a component of a standard prokaryotic Operon?
A An Operator
B Structural Genes
C An Enhancer
D A Promoter
In the Lac Operon system, the hydrolysis of disaccharide lactose into monomeric galactose and glucose is catalyzed by the product of which gene?
A a-gene
B i-gene
C l-gene
D z-gene
In the regulation of the Lac Operon, which specific molecule acts as the “Inducer” by binding to the repressor and inactivating it?
A Tryptophan
B Lactose (or Allolactose)
C Glucose
D Galactose
The Human Genome Project used a specific approach called “Expressed Sequence Tags” (ESTs). What does this approach strictly focus on?
A Sequencing the entire genome blindly.
B Identifying all genes that are expressed as RNA.
C Identifying only disease-causing mutations.
D Sequencing only the introns.
Which of the following techniques is NOT a prerequisite step or tool for DNA Fingerprinting?
A Digestion by Restriction Enzymes.
B DNA-DNA Hybridization.
C Polymerase Chain Reaction (PCR).
D Zinc Finger Analysis.
Why is Satellite DNA considered the critical tool for DNA fingerprinting?
A Because it codes for essential enzymes needed for replication.
B Because it is the same in all members of a population.
C Because it shows a high degree of polymorphism that is heritable.
D Because it contains the “Start” and “Stop” signals for genes.
Identify the correct order of organization of genetic material from the largest unit to the smallest unit:
A Genome, Chromosome, Gene, Nucleotide
B Chromosome, Genome, Nucleotide, Gene
C Chromosome, Gene, Genome, Nucleotide
D Genome, Chromosome, Nucleotide, Gene
The classic DNA fingerprinting technique developed by Alec Jeffreys uses a specific type of satellite DNA probe called:
A VNTR (Variable Number of Tandem Repeats)
B SSCP (Single Strand Conformation Polymorphism)
C SCAR (Sequence Characterized Amplified Region)
D AFLP (Amplified Fragment Length Polymorphism)
What is the genetic material found in the Tobacco Mosaic Virus (TMV)?
A Double-stranded DNA
B Single-stranded RNA
C Double-stranded RNA
D Single-stranded DNA
Thomas Hunt Morgan used a specific experimental organism to prove the chromosomal theory of inheritance. Which organism was it?
A Neurospora crassa
B Drosophila melanogaster
C E. coli
D Pisum sativum
In the process of DNA isolation, the addition of Chilled Ethanol serves which specific function?
A Digestion of the cell wall.
B Removal of RNA.
C Precipitation of DNA.
D Denaturation of proteins.
Consider the following statements regarding DNA Fingerprinting:
Assertion (A): DNA fingerprinting can resolve paternity disputes.
Reason (R): Polymorphisms in Satellite DNA are inheritable from parents to children.
A Both A and R are true, and R explains A
B Both A and R are true, but R does not explain A
C A is true, but R is false
D A is false, but R is true

Quick Revision: Key Facts

Packaging Ratio: The 2.2-meter DNA fits into a nucleus using Histone Octamers (H2A, H2B, H3, H4) and H1 linker.
Chargaff’s Rule: In dsDNA, Purines (A+G) always equal Pyrimidines (T+C).
Replication Fork: DNA Polymerase polymerizes only in 5′->3′; thus, the lagging strand is discontinuous (Okazaki fragments).
Central Dogma: DNA -> (Transcription) -> mRNA -> (Translation) -> Protein. Exception: Reverse Transcription in Retroviruses.

Frequently Asked Questions

Why is Molecular basis of inheritance MCQ critical for NCERT Class 12 Biology Exam?
It is a high-yield topic. Analyzing previous year papers of NCERT Class 12 Biology Exam shows a consistent trend of questions from this area.
Is this content updated?
Yes, these questions reflect the latest pattern and recent judicial interpretations relevant for the exam.

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