Advertisement
11-12th Class

Molecular Basis of Inheritance In Easy Notes

Afifa Asad 0

Meta Description:
Comprehensive notes on the Molecular Basis of Inheritance for Class 12 Biology. Includes summary, diagrams, keywords, MCQs, important questions, and exam tips for board and competitive exams.

Introduction of the Chapter

The chapter Molecular Basis of Inheritance explains how genetic information is stored, copied, and expressed in living organisms. It focuses on DNA as the genetic material, its structure, replication, transcription, translation, and regulation of gene expression.

Understanding the Molecular Basis of Inheritance helps students learn how traits pass from parents to offspring at the molecular level. It forms the foundation for biotechnology, genetic engineering, forensic science, and modern medicine.

This chapter is highly important for board exams and competitive exams like NEET.

Short Notes

  • DNA and RNA are nucleic acids responsible for heredity.
  • DNA acts as the genetic material in most organisms.
  • RNA acts as genetic material in some viruses.
  • DNA structure was proposed by Watson and Crick.
  • DNA replication is semiconservative.
  • Transcription is synthesis of RNA from DNA.
  • Translation forms proteins using mRNA.
  • Genetic code is universal and degenerate.
  • Operon model explains gene regulation in prokaryotes.
  • Human Genome Project mapped all human genes.
  • DNA fingerprinting identifies individuals.

Detailed Summary (Molecular Basis of Inheritance)

The Molecular Basis of Inheritance chapter explains how genetic information is stored and transmitted through DNA and expressed as proteins. Experiments by Griffith demonstrated transformation, suggesting a “transforming principle” responsible for transferring genetic traits. Avery, MacLeod, and McCarty later confirmed DNA as the genetic material. Hershey and Chase proved this using bacteriophages.

DNA as Genetic Material

DNA is stable, capable of replication, and able to express itself through proteins, making it ideal genetic material. In some viruses, RNA acts as genetic material due to absence of DNA.

Structure of DNA

Watson and Crick proposed the double helix model of DNA. It consists of two antiparallel strands made of nucleotides. Each nucleotide contains:

  • Nitrogenous base (A, T, G, C)
  • Deoxyribose sugar
  • Phosphate group

Base pairing follows Chargaff’s rule:

  • Adenine pairs with Thymine (2 hydrogen bonds)
  • Guanine pairs with Cytosine (3 hydrogen bonds)

The helix has a diameter of 20 Å and one turn every 34 Å with 10 base pairs per turn.

Packaging of DNA

In prokaryotes, DNA is negatively supercoiled. In eukaryotes, DNA wraps around histone proteins forming nucleosomes. This packaging helps fit DNA into the nucleus.

DNA Replication

DNA replication is semiconservative, meaning each new DNA contains one parental strand and one new strand. It occurs during S-phase of the cell cycle.

Steps include:

  1. Unwinding by helicase
  2. Primer formation by primase
  3. DNA synthesis by DNA polymerase
  4. Leading and lagging strand synthesis
  5. Joining fragments by ligase

Transcription

Transcription is the process of synthesizing RNA from DNA.

Types of RNA:

  • mRNA: carries genetic message
  • tRNA: brings amino acids
  • rRNA: forms ribosomes

Process:

  • Initiation at promoter
  • Elongation by RNA polymerase
  • Termination at stop sequence

In eukaryotes, RNA undergoes splicing, capping, and tailing.

Genetic Code

The genetic code translates nucleotide sequences into amino acids.

Properties:

  • Triplet code
  • Degenerate
  • Universal
  • Non-overlapping
  • Start codon: AUG
  • Stop codons: UAA, UAG, UGA

Translation (Protein Synthesis)

Translation occurs in ribosomes.

Steps:

  1. Activation of amino acids
  2. Initiation at start codon
  3. Elongation of polypeptide chain
  4. Termination at stop codon

Regulation of Gene Expression (Operon Model)

Jacob and Monod proposed the lac operon model in bacteria.

Components:

  • Regulator gene
  • Promoter
  • Operator
  • Structural genes

Lactose activates genes required for its metabolism.

Human Genome Project (HGP)

The Human Genome Project mapped the entire human DNA sequence.

Findings:

  • Humans have about 20,000–25,000 genes.
  • Only about 2% DNA codes for proteins.
  • Genetic similarity among humans is 99.9%.

DNA Fingerprinting

Developed by Alec Jeffreys, DNA fingerprinting identifies individuals using VNTR sequences. It is used in forensic science, paternity testing, and crime investigation.

The Molecular Basis of Inheritance chapter connects molecular genetics with real-life applications, making it crucial for modern biology.

Flowchart / Mind Map

Molecular Basis of Inheritance

DNA as Genetic Material
→ Griffith → Avery → Hershey & Chase

Structure of DNA
→ Double helix → Base pairing → Chargaff rule

DNA Replication
→ Helicase → Polymerase → Ligase

Transcription
→ DNA → RNA

Translation
→ mRNA → Protein

Genetic Code
→ Triplet → Universal

Gene Regulation
→ Lac Operon

Applications
→ Human Genome Project → DNA Fingerprinting

Important Keywords with Meanings

  • DNA – Genetic material carrying hereditary information
  • Nucleotide – Basic unit of nucleic acids
  • Replication – DNA copying process
  • Transcription – RNA synthesis from DNA
  • Translation – Protein formation from mRNA
  • Codon – Triplet code for amino acids
  • Operon – Gene regulation unit in prokaryotes
  • VNTR – Variable number tandem repeats used in fingerprinting
  • Genome – Complete genetic material of an organism
  • Semiconservative replication – Each DNA contains one old and one new strand

Important Questions & Answers

Short Answer Questions

  1. What is the transforming principle?
    DNA responsible for transferring genetic traits.
  2. Who proposed the double helix model?
    Watson and Crick.
  3. What is semiconservative replication?
    Each daughter DNA has one old and one new strand.
  4. Name three types of RNA.
    mRNA, tRNA, rRNA.
  5. What is a codon?
    Triplet of nucleotides coding for one amino acid.
  6. What is the start codon?
    AUG.
  7. Define transcription.
    Formation of RNA from DNA template.
  8. What is VNTR?
    Repeated DNA sequences used in fingerprinting.
  9. Where does translation occur?
    Ribosomes.
  10. What is the Human Genome Project?
    Project to map all human genes.

Long Answer Questions

  1. Explain experiments proving DNA as genetic material.
    Answer: Griffith discovered transformation; Avery proved DNA responsible; Hershey & Chase confirmed using bacteriophages.
  2. Describe Watson and Crick model of DNA.
    Answer: Double helix, antiparallel strands, complementary base pairing, helical structure.
  3. Explain DNA replication.
    Answer: Semiconservative process involving helicase, polymerase, ligase, leading & lagging strands.
  4. Describe transcription in eukaryotes.
    Answer: RNA synthesis followed by splicing, capping, and poly-A tail formation.
  5. Explain translation process.
    Answer: Ribosomes decode mRNA to synthesize proteins.
  6. Write properties of genetic code.
    Answer: Triplet, universal, degenerate, non-overlapping.
  7. Explain lac operon model.
    Answer: Regulates lactose metabolism genes in bacteria.
  8. Write notes on DNA packaging.
    Answer: DNA wraps around histones forming nucleosomes.
  9. Explain Human Genome Project findings.
    Answer: 20–25k genes; only small fraction codes proteins.
  10. Describe DNA fingerprinting and its uses.
    Answer: Identifies individuals; used in forensics and paternity testing.

MCQs with Answers

  1. DNA structure proposed by:
    A. Mendel
    B. Watson & Crick
    C. Darwin
    D. Pasteur
    Answer: B
  2. Base pairing rule discovered by:
    A. Chargaff
    B. Mendel
    C. Darwin
    D. Lamarck
    Answer: A
  3. Genetic material in viruses may be:
    A. Protein
    B. RNA
    C. Lipid
    D. Carbohydrate
    Answer: B
  4. DNA replication is:
    A. Conservative
    B. Dispersive
    C. Semiconservative
    D. Random
    Answer: C
  5. RNA synthesis is called:
    A. Replication
    B. Translation
    C. Transcription
    D. Mutation
    Answer: C
  6. Start codon is:
    A. UAA
    B. AUG
    C. UGA
    D. UAG
    Answer: B
  7. Stop codon example:
    A. AUG
    B. UUU
    C. UGA
    D. GGG
    Answer: C
  8. Site of protein synthesis:
    A. Nucleus
    B. Ribosome
    C. Golgi body
    D. Lysosome
    Answer: B
  9. DNA fingerprinting developed by:
    A. Watson
    B. Alec Jeffreys
    C. Darwin
    D. Mendel
    Answer: B
  10. Operon model proposed by:
    A. Jacob & Monod
    B. Watson
    C. Mendel
    D. Pasteur
    Answer: A
  11. DNA is made of repeating units called: Nucleotides
  12. Human genome similarity among individuals: 99.9%
  13. Number of base pairs per turn: 10
  14. Hydrogen bonds in A-T: 2
  15. Hydrogen bonds in G-C: 3
  16. Enzyme that joins DNA fragments: Ligase
  17. RNA processing occurs in: Eukaryotes
  18. Functional unit of gene regulation: Operon
  19. mRNA carries message from: DNA to ribosome
  20. VNTR used in: DNA fingerprinting

Exam Tips & Value-Based Questions

Exam Tips

  • Learn diagrams of DNA structure and replication.
  • Remember key scientists and experiments.
  • Understand processes stepwise.
  • Practice genetic code table.
  • Revise lac operon and applications.

Value-Based Questions

  1. Why is DNA fingerprinting useful in crime investigation?
    → Helps identify criminals accurately.
  2. How does genetic research help in disease treatment?
    → Enables gene therapy and diagnosis.
  3. Why is genome mapping important for humanity?
    → Helps understand genetic disorders.
  4. How does biotechnology improve agriculture?
    → Produces disease-resistant crops.
  5. Why should genetic data be used ethically?
    → To protect privacy and prevent misuse.

Conclusion

The chapter Molecular Basis of Inheritance provides a deep understanding of how genetic information is stored, transmitted, and expressed at the molecular level. It explains DNA as the hereditary material, its structure, replication, and functioning in protein synthesis.

This chapter connects classical genetics with molecular biology, helping students understand life processes at the cellular level. Concepts like DNA replication, transcription, translation, genetic code, and gene regulation form the backbone of modern biology.

The Molecular Basis of Inheritance also introduces groundbreaking applications such as DNA fingerprinting, genome mapping, and biotechnology. These advancements play vital roles in medicine, agriculture, forensic science, and evolutionary studies.

Mastering this chapter helps students perform well in board exams and competitive exams. Understanding the Molecular Basis of Inheritance strengthens conceptual clarity and prepares learners for advanced topics in genetics and biotechnology.

With clear knowledge of molecular genetics, students gain insight into how traits are inherited, how mutations occur, and how gene expression shapes living organisms. This makes the Molecular Basis of Inheritance one of the most important chapters in Class 12 Biology.

Assertion–Reason Questions: Molecular Basis of Inheritance

Directions:
For each question, choose the correct option:

A. Both Assertion and Reason are true, and Reason is the correct explanation of Assertion.
B. Both Assertion and Reason are true, but Reason is not the correct explanation of Assertion.
C. Assertion is true, but Reason is false.
D. Assertion is false, but Reason is true.

1.

Assertion (A): DNA is considered the genetic material in most organisms.
Reason (R): DNA is stable and capable of replication and expression.

Answer: A

2.

Assertion (A): RNA can act as genetic material in some viruses.
Reason (R): These viruses lack DNA.

Answer: A

3.

Assertion (A): In DNA, adenine pairs with thymine.
Reason (R): Adenine and thymine form two hydrogen bonds.

Answer: A

4.

Assertion (A): DNA replication is semiconservative.
Reason (R): Each daughter DNA molecule contains one parental and one newly synthesized strand.

Answer: A

5.

Assertion (A): Lagging strand synthesis is discontinuous.
Reason (R): DNA polymerase synthesizes DNA only in the 5′ → 3′ direction.

Answer: A

6.

Assertion (A): Transcription produces mRNA from DNA.
Reason (R): RNA polymerase reads the DNA template strand.

Answer: A

7.

Assertion (A): Genetic code is said to be degenerate.
Reason (R): More than one codon can code for the same amino acid.

Answer: A

8.

Assertion (A): Translation occurs in ribosomes.
Reason (R): Ribosomes contain rRNA and proteins essential for protein synthesis.

Answer: A

9.

Assertion (A): Lac operon is activated in the presence of lactose.
Reason (R): Lactose acts as an inducer by inactivating the repressor protein.

Answer: A

10.

Assertion (A): DNA fingerprinting can identify individuals.
Reason (R): Individuals differ in the number of VNTR sequences in their DNA.

Answer: A

Unseen Passage

Unseen Passage: Molecular Basis of Inheritance

Read the passage carefully and answer the questions that follow.

Scientists have long sought to understand how genetic information is stored and transmitted from one generation to the next. Early experiments suggested that some “transforming principle” was responsible for transferring traits between organisms. Later research confirmed that DNA carries hereditary information. DNA is composed of nucleotides containing a sugar, phosphate group, and nitrogenous base. The bases pair specifically (adenine with thymine and guanine with cytosine), allowing accurate copying of genetic material.

During cell division, DNA replicates to ensure that each daughter cell receives identical genetic information. This replication follows a semiconservative pattern, where each new DNA molecule contains one parental strand and one newly synthesized strand. The sequence of bases in DNA determines the sequence of amino acids in proteins.

The process of transcription converts DNA information into messenger RNA (mRNA), which carries the code from the nucleus to the ribosome. During translation, ribosomes read the mRNA codons and assemble amino acids into proteins. The genetic code is universal, meaning most organisms use the same codons to specify amino acids.

In prokaryotes, gene expression is regulated through operons such as the lac operon, which controls lactose metabolism. When lactose is present, genes required for its breakdown are activated. Advances in molecular genetics have also led to technologies like DNA fingerprinting, which uses repetitive DNA sequences to identify individuals.

Questions

Very Short Answer

  1. What is meant by the “transforming principle”?
    Answer: The substance responsible for transferring genetic traits; later identified as DNA.
  2. Name the complementary base pairs in DNA.
    Answer: Adenine–Thymine and Guanine–Cytosine.
  3. What type of replication does DNA undergo?
    Answer: Semiconservative replication.
  4. Which RNA carries genetic information to ribosomes?
    Answer: mRNA.
  5. Where does translation occur?
    Answer: Ribosomes.

Short Answer Questions

  1. Why is base pairing important in DNA replication?
    Answer: Complementary base pairing ensures accurate copying of genetic information.
  2. What is the role of mRNA in protein synthesis?
    Answer: It carries genetic code from DNA to ribosomes for protein formation.
  3. What is meant by the universal nature of genetic code?
    Answer: Most organisms use the same codons to code for amino acids.
  4. How does lactose regulate the lac operon?
    Answer: Lactose inactivates the repressor, allowing gene expression.
  5. What is the basis of DNA fingerprinting?
    Answer: Variation in repetitive DNA sequences (VNTRs) among individuals.

Long Answer / Application-Based Questions

  1. Explain how DNA structure helps in accurate replication.
    Answer: Complementary base pairing and double helix structure allow each strand to serve as a template, ensuring precise replication.
  2. Describe the relationship between DNA, RNA, and protein synthesis.
    Answer: DNA stores genetic information → transcription produces RNA → translation converts RNA code into proteins.
  3. Why is semiconservative replication important for inheritance?
    Answer: It ensures genetic continuity by preserving one parental strand in each new DNA molecule.
  4. Explain how gene regulation helps bacteria adapt to environmental changes.
    Answer: Operon systems activate genes only when needed, conserving energy and enabling adaptation.
  5. Suggest two applications of molecular genetics in modern society.
    Answer: Forensic identification using DNA fingerprinting and diagnosis of genetic disorders.

Sample Question Paper

Class 12 Biology

Chapter: Molecular Basis of Inheritance

Time: 3 Hours
Maximum Marks: 70

Section A: Multiple Choice Questions (1 × 10 = 10 Marks)

  1. The transforming principle was discovered by:
    a) Mendel
    b) Griffith
    c) Darwin
    d) Watson
    Answer: b
  2. DNA replication is:
    a) Conservative
    b) Dispersive
    c) Semiconservative
    d) Random
    Answer: c
  3. Which enzyme synthesizes DNA?
    a) Helicase
    b) Ligase
    c) DNA polymerase
    d) Primase
    Answer: c
  4. Start codon is:
    a) UAA
    b) AUG
    c) UAG
    d) UGA
    Answer: b
  5. The number of hydrogen bonds between G and C is:
    a) 1
    b) 2
    c) 3
    d) 4
    Answer: c
  6. RNA polymerase is involved in:
    a) Replication
    b) Transcription
    c) Translation
    d) Mutation
    Answer: b
  7. Genetic code is called degenerate because:
    a) It is universal
    b) Multiple codons code same amino acid
    c) Codons overlap
    d) It is continuous
    Answer: b
  8. VNTRs are used in:
    a) Cloning
    b) DNA fingerprinting
    c) Protein synthesis
    d) Respiration
    Answer: b
  9. The functional unit of gene regulation in bacteria is:
    a) Codon
    b) Operon
    c) Nucleosome
    d) Ribosome
    Answer: b
  10. Site of protein synthesis is:
    a) Nucleus
    b) Ribosome
    c) Golgi body
    d) Lysosome
    Answer: b

Section B: Very Short Answer (2 × 10 = 20 Marks)

  1. Define nucleotide.
  2. What is semiconservative replication?
  3. Name the scientist who proposed the double helix model.
  4. What is a codon?
  5. Mention two types of RNA.
  6. What is transcription?
  7. Write the base pairing rule.
  8. What is the role of ligase enzyme?
  9. Define genome.
  10. What is DNA fingerprinting?

Section C: Short Answer Questions (3 × 6 = 18 Marks)

  1. Explain the Hershey and Chase experiment.
  2. Write the structure of a nucleotide.
  3. Differentiate between leading and lagging strands.
  4. Explain the role of tRNA in translation.
  5. What are stop codons? Name them.
  6. Write two features of the genetic code.

Section D: Long Answer Questions (5 × 4 = 20 Marks)

  1. Describe the Watson and Crick model of DNA.
  2. Explain the process of DNA replication.
  3. Describe transcription in eukaryotes.
  4. Explain the lac operon model of gene regulation.

Section E: Case-Based Question (4 Marks)

A scientist observed that when bacteria were grown in a medium containing lactose, enzymes required for lactose metabolism were produced. However, these enzymes were not produced when lactose was absent.

Questions:

a) Name the model that explains this regulation.
b) What role does lactose play in this mechanism?
c) Name the gene that produces the repressor protein.
d) Why is this regulation beneficial to bacteria?

Internal Choice Questions

  • Explain translation in place of transcription.
  • Write applications of DNA fingerprinting in place of lac operon.

Solution: Sample Question Paper

Chapter — Molecular Basis of Inheritance

Section A: Multiple Choice Questions

  1. Griffith discovered transforming principle → b) Griffith
  2. DNA replication type → c) Semiconservative
  3. Enzyme that synthesizes DNA → c) DNA polymerase
  4. Start codon → b) AUG
  5. Hydrogen bonds in G–C → c) 3
  6. RNA polymerase function → b) Transcription
  7. Degenerate genetic code means → b) Multiple codons code same amino acid
  8. VNTRs used in → b) DNA fingerprinting
  9. Functional unit of gene regulation → b) Operon
  10. Site of protein synthesis → b) Ribosome

Section B: Very Short Answers

  1. Nucleotide: Basic unit of nucleic acids consisting of nitrogenous base, sugar, and phosphate group.
  2. Semiconservative replication: Each daughter DNA contains one parental strand and one newly synthesized strand.
  3. Double helix model proposed by: Watson and Crick.
  4. Codon: A triplet of nucleotides on mRNA coding for one amino acid.
  5. Two types of RNA: mRNA and tRNA. (rRNA also correct)
  6. Transcription: Formation of RNA from DNA template.
  7. Base pairing rule: Adenine pairs with Thymine; Guanine pairs with Cytosine.
  8. Role of ligase: Joins Okazaki fragments on lagging strand.
  9. Genome: Complete set of genetic material in an organism.
  10. DNA fingerprinting: Technique used to identify individuals using unique DNA patterns.

Section C: Short Answer Questions

1. Hershey and Chase Experiment

They used bacteriophages with radioactive sulfur (protein) and phosphorus (DNA). Only DNA entered bacterial cells and directed virus replication, proving DNA is genetic material.

2. Structure of a Nucleotide

A nucleotide consists of:

  • Nitrogenous base (A, T, G, C)
  • Pentose sugar (deoxyribose)
  • Phosphate group

3. Leading vs Lagging Strand

FeatureLeading StrandLagging Strand
SynthesisContinuousDiscontinuous
DirectionToward replication forkAway from fork
FragementsNoneOkazaki fragments

4. Role of tRNA in Translation

tRNA carries specific amino acids to the ribosome and matches anticodon with mRNA codon to ensure correct protein synthesis.

5. Stop Codons

They terminate protein synthesis.
UAA, UAG, UGA

6. Features of Genetic Code

  • Triplet code
  • Universal
  • Degenerate
  • Non-overlapping

Section D: Long Answer Questions

1. Watson and Crick Model of DNA

  • DNA is a double helix.
  • Two antiparallel strands run in opposite directions.
  • Sugar-phosphate backbone forms the outer structure.
  • Nitrogen bases pair internally (A–T, G–C).
  • Helix diameter: 20 Å; 10 base pairs per turn.

2. DNA Replication Process

DNA replication is semiconservative and occurs in S phase.

Steps:

  1. Helicase unwinds DNA.
  2. Primase forms RNA primers.
  3. DNA polymerase synthesizes new strands.
  4. Leading strand forms continuously.
  5. Lagging strand forms Okazaki fragments.
  6. Ligase joins fragments.

3. Transcription in Eukaryotes

  • RNA polymerase synthesizes pre-mRNA.
  • Post-transcription modifications:
    • 5′ capping
    • Poly-A tailing
    • Splicing (removal of introns)
  • Mature mRNA moves to cytoplasm for translation.

4. Lac Operon Model

Proposed by Jacob and Monod.

Components:

  • Regulator gene (produces repressor)
  • Promoter
  • Operator
  • Structural genes

Mechanism:

  • Without lactose → repressor blocks transcription.
  • With lactose → repressor inactivated → genes expressed.

Section E: Case-Based Question

a) Name the model:
Lac operon model.

b) Role of lactose:
Acts as an inducer; inactivates the repressor protein.

c) Gene producing repressor protein:
Regulator gene (lacI).

d) Why regulation is beneficial:
It saves energy by producing enzymes only when lactose is present.

Internal Choice Answers

Explain Translation

Translation is protein synthesis at ribosomes where mRNA codons are read and amino acids are joined to form a polypeptide chain with help of tRNA.

Applications of DNA Fingerprinting

  • Crime investigation
  • Paternity testing
  • Identification of disaster victims
  • Wildlife conservation

Additional Sample paper

Class 12 Biology

Chapter: Molecular Basis of Inheritance

Time: 3 Hours
Maximum Marks: 70

Section A: Multiple Choice Questions (1 × 10 = 10 Marks)

  1. Chargaff’s rule states that:
    a) A = G, T = C
    b) A = T, G = C
    c) A + T = G + C
    d) A ≠ T, G ≠ C
  2. Which of the following is NOT a type of RNA?
    a) mRNA
    b) tRNA
    c) rRNA
    d) dRNA
  3. Which enzyme unwinds the DNA helix during replication?
    a) Ligase
    b) Helicase
    c) Polymerase
    d) Topoisomerase
  4. Okazaki fragments are found on:
    a) Leading strand
    b) Lagging strand
    c) Both strands
    d) mRNA
  5. Which codon signals the start of translation?
    a) UAA
    b) UAG
    c) AUG
    d) UGA
  6. VNTR stands for:
    a) Variable number tandem repeats
    b) Variable nucleotide transcription repeats
    c) Very normal tandem repeat
    d) Variable nucleotide transfer RNA
  7. Who discovered the lac operon?
    a) Watson & Crick
    b) Jacob & Monod
    c) Griffith
    d) Hershey & Chase
  8. In eukaryotes, which process removes introns from RNA?
    a) Capping
    b) Tailing
    c) Splicing
    d) Replication
  9. The Human Genome Project was completed in:
    a) 1980
    b) 1990
    c) 2003
    d) 2010
  10. DNA fingerprinting is mainly used in:
    a) Protein synthesis
    b) Cell division
    c) Forensic science
    d) RNA processing

Section B: Very Short Answer (2 × 10 = 20 Marks)

  1. Define genetic material.
  2. Name the three components of a nucleotide.
  3. What is the function of DNA polymerase?
  4. Define transcription and translation.
  5. What is an anticodon?
  6. Name the three stop codons.
  7. Write one feature of the genetic code.
  8. Define operon.
  9. What is the role of tRNA in protein synthesis?
  10. Give one application of DNA fingerprinting.

Section C: Short Answer Questions (3 × 6 = 18 Marks)

  1. Explain the Avery–MacLeod–McCarty experiment.
  2. Compare RNA and DNA.
  3. Differentiate between prokaryotic and eukaryotic transcription.
  4. Explain the semiconservative model of DNA replication.
  5. Mention any three properties of the genetic code.
  6. Write a note on human genome mapping.

Section D: Long Answer Questions (5 × 4 = 20 Marks)

  1. Describe the structure of DNA and explain how it facilitates replication.
  2. Explain the process of transcription in eukaryotes.
  3. Explain translation process with a diagrammatic sequence.
  4. Explain the lac operon mechanism of gene regulation in bacteria.
  5. Discuss the applications of molecular genetics in modern biology.

Section E: Case-Based Question (4 Marks)

A forensic scientist collected blood samples from a crime scene. Using DNA analysis, they were able to identify the suspect. The technique used repetitive DNA sequences that are unique in every individual.

Questions:
a) Name the technique used.
b) What are VNTRs?
c) How does this technique help in forensic science?
d) Why are repetitive DNA sequences useful for identification?

Internal Choice Questions

  • Explain the role of ribosomes in translation.
  • Write the differences between DNA and RNA.

Solution: Additional Sample Paper

Chapter — Molecular Basis of Inheritance

Section A: Multiple Choice Questions

  1. Chargaff’s rule → b) A = T, G = C
  2. Not a type of RNA → d) dRNA
  3. Enzyme that unwinds DNA → b) Helicase
  4. Okazaki fragments → b) Lagging strand
  5. Start codon → c) AUG
  6. VNTR → a) Variable number tandem repeats
  7. Lac operon discovered by → b) Jacob & Monod
  8. Removes introns → c) Splicing
  9. Human Genome Project completed → c) 2003
  10. DNA fingerprinting used in → c) Forensic science

Section B: Very Short Answer

  1. Genetic material: Substance in cells responsible for heredity (DNA in most organisms, RNA in some viruses).
  2. Three components of a nucleotide: Nitrogenous base, pentose sugar, phosphate group.
  3. DNA polymerase function: Synthesizes new DNA strand by adding nucleotides.
  4. Transcription: Synthesis of RNA from DNA.
    Translation: Synthesis of proteins from mRNA.
  5. Anticodon: A triplet of nucleotides on tRNA that pairs with a complementary mRNA codon.
  6. Stop codons: UAA, UAG, UGA.
  7. Feature of genetic code: Universal — same codons specify same amino acids in almost all organisms.
  8. Operon: A functional unit of genes under a single promoter in prokaryotes that regulates gene expression.
  9. Role of tRNA: Transfers specific amino acids to the ribosome and matches anticodon to mRNA codon during protein synthesis.
  10. Application of DNA fingerprinting: Crime investigation, paternity testing, forensic identification.

Section C: Short Answer Questions

  1. Avery–MacLeod–McCarty experiment:
    They isolated DNA, RNA, and proteins from pneumococcus bacteria. Only DNA caused transformation in non-virulent bacteria, proving DNA is the hereditary material.
  2. Comparison of RNA and DNA:
FeatureDNARNA
SugarDeoxyriboseRibose
StrandsDoubleSingle
BasesA, T, G, CA, U, G, C
FunctionGenetic materialProtein synthesis, sometimes genetic material in viruses
  1. Prokaryotic vs Eukaryotic Transcription:
FeatureProkaryotesEukaryotes
LocationCytoplasmNucleus
mRNA processingNoneCapping, tailing, splicing
RNA polymerasesSingleMultiple (I, II, III)
  1. Semiconservative DNA replication:
    Each daughter DNA has one parental and one newly synthesized strand. Confirmed by Meselson and Stahl experiment using N¹⁵-labeled DNA.
  2. Properties of genetic code:
  • Triplet code
  • Degenerate
  • Universal
  • Non-overlapping
  • Start and stop codons
  1. Human genome mapping:
    Human Genome Project mapped all human genes (~20,000–25,000 genes) and identified sequences responsible for genetic disorders. Only 2% of DNA codes for proteins.

Section D: Long Answer Questions

  1. Structure of DNA and its replication:
  • Double helix, antiparallel strands.
  • Sugar-phosphate backbone outside, bases inside.
  • Base pairing allows semiconservative replication.
  • Each strand acts as a template for new DNA.
  1. Transcription in eukaryotes:
  • RNA polymerase synthesizes pre-mRNA from DNA template.
  • Post-transcriptional modifications:
    • 5′ cap
    • Poly-A tail
    • Splicing (introns removed, exons joined)
  • mRNA moves to cytoplasm for translation.
  1. Translation process:
  • Occurs in ribosomes.
  • Steps:
    1. Activation of amino acids by tRNA.
    2. Initiation: ribosome assembles at start codon AUG.
    3. Elongation: amino acids linked via peptide bonds.
    4. Termination: Stop codon signals end of polypeptide.
  1. Lac operon mechanism:
  • Regulator gene produces repressor protein.
  • In absence of lactose: repressor binds operator → blocks transcription.
  • In presence of lactose: repressor inactivated → genes transcribed → enzymes metabolize lactose.
  1. Applications of molecular genetics:
  • DNA fingerprinting: crime and paternity tests
  • Human Genome Project: identify genetic disorders
  • Gene therapy: treatment of inherited diseases
  • Biotechnology: genetically modified crops

Section E: Case-Based Question

a) Technique used: DNA fingerprinting.
b) VNTRs: Variable Number Tandem Repeats; repetitive sequences unique to individuals.
c) Forensic use: Identifies criminals or victims accurately.
d) Why repetitive DNA useful: High variability ensures unique pattern for each individual.

Internal Choice Solutions

Role of ribosomes in translation:
Ribosomes facilitate decoding of mRNA codons and formation of peptide bonds between amino acids to synthesize proteins.

Differences between DNA and RNA: (Refer Section C, Q2 table)

Related Story

Leave a Reply

Your email address will not be published. Required fields are marked *