Chapter 6: Molecular Basis of Inheritance – Very Short Answer Type Questions

CBSE Class 12 Biology Very Short Answer Questions (NCERT): Molecular Basis of Inheritance

Course & Examination Details

Course: CBSE Class 12 Biology
Unit: Unit II – Genetics and Evolution
Chapter: Chapter 6 – Molecular Basis of Inheritance
Prescribed Textbook: NCERT Biology Class XII
Examination: CBSE Class 12 Board Examination
Question Type: Very Short Answer Type (VSA)
Answer Length: 20–30 words each

Section A: DNA as Genetic Material

Q1. What properties must a molecule possess to act as genetic material?

Answer: Genetic material must be stable, capable of replication, able to mutate, and capable of expressing information as phenotype.

Q2. Why is DNA considered a better genetic material than RNA?

Answer: DNA is more stable due to deoxyribose sugar and double-stranded structure, which allows error correction and long-term information storage.

Q3. Which experiment proved DNA as genetic material?

Answer: The Hershey–Chase experiment proved DNA, not protein, is the genetic material in bacteriophages.

Q4. In which organisms is RNA the genetic material?

Answer: RNA acts as genetic material in certain viruses such as tobacco mosaic virus and retroviruses.

Q5. What is meant by transforming principle?

Answer: Transforming principle refers to a substance that transfers genetic information from one organism to another.

Section B: Structure of DNA and RNA

Q6. Who proposed the double helix model of DNA?

Answer: James Watson and Francis Crick proposed the double helix model of DNA.

Q7. What are the components of a DNA nucleotide?

Answer: A DNA nucleotide consists of deoxyribose sugar, phosphate group, and a nitrogenous base.

Q8. Name the nitrogenous bases present in DNA.

Answer: Adenine, Guanine, Cytosine, and Thymine are the nitrogenous bases present in DNA.

Q9. What type of bonds join nucleotides in a DNA strand?

Answer: Phosphodiester bonds join adjacent nucleotides in a DNA strand.

Q10. How does RNA differ from DNA structurally?

Answer: RNA is single-stranded, contains ribose sugar, and has uracil instead of thymine.

Section C: Replication of DNA

Q11. What is DNA replication?

Answer: DNA replication is the process of copying DNA to produce two identical DNA molecules before cell division.

Q12. What is meant by semi-conservative replication?

Answer: Each daughter DNA molecule contains one parental strand and one newly synthesized strand.

Q13. Which enzyme unwinds the DNA helix during replication?

Answer: DNA helicase unwinds the DNA double helix during replication.

Q14. Why are Okazaki fragments formed?

Answer: Okazaki fragments form on the lagging strand because DNA synthesis occurs discontinuously in the 5′ to 3′ direction.

Q15. Which enzyme joins Okazaki fragments?

Answer: DNA ligase joins Okazaki fragments to form a continuous DNA strand.

Section D: Transcription

Q16. What is transcription?

Answer: Transcription is the synthesis of RNA from a DNA template by RNA polymerase.

Q17. Which strand of DNA acts as template in transcription?

Answer: The template strand, oriented in 3′ to 5′ direction, acts as the template for transcription.

Q18. Name the enzyme involved in transcription.

Answer: RNA polymerase is the enzyme responsible for transcription.

Q19. Why is transcription asymmetric?

Answer: Only one strand of DNA is transcribed to avoid formation of complementary RNA molecules.

Q20. Which base replaces thymine in RNA?

Answer: Uracil replaces thymine in RNA.

Section E: Genetic Code

Q21. What is a codon?

Answer: A codon is a triplet sequence of nucleotides on mRNA that codes for a specific amino acid.

Q22. Why is genetic code called degenerate?

Answer: Genetic code is degenerate because more than one codon can code for the same amino acid.

Q23. Name the start codon.

Answer: AUG is the start codon and codes for methionine.

Q24. What are stop codons?

Answer: Stop codons are UAA, UAG, and UGA, which signal termination of protein synthesis.

Q25. Why is genetic code considered universal?

Answer: The same genetic code operates in almost all organisms, from bacteria to humans.

Section F: Translation

Q26. What is translation?

Answer: Translation is the synthesis of a polypeptide chain from mRNA using ribosomes and tRNA.

Q27. Which molecule acts as an adaptor during translation?

Answer: tRNA acts as an adaptor molecule by bringing specific amino acids to the ribosome.

Q28. What is the function of ribosomes?

Answer: Ribosomes are sites of protein synthesis and facilitate peptide bond formation.

Q29. What is an anticodon?

Answer: Anticodon is a triplet of nucleotides on tRNA complementary to the codon on mRNA.

Q30. Which bond joins amino acids in a polypeptide?

Answer: Peptide bonds join amino acids in a growing polypeptide chain.

Section G: Regulation of Gene Expression

Q31. What is gene regulation?

Answer: Gene regulation is the control of gene expression to ensure proteins are synthesized only when required.

Q32. What is an operon?

Answer: An operon is a functional unit of gene regulation in prokaryotes consisting of structural genes, promoter, and operator.

Q33. Which operon explains inducible gene expression?

Answer: The lac operon explains inducible gene expression in prokaryotes.

Q34. What is the role of repressor protein in lac operon?

Answer: Repressor protein binds to operator and prevents transcription in absence of lactose.

Q35. What happens to lac operon in presence of lactose?

Answer: Lactose inactivates the repressor, allowing transcription of structural genes.

Section H: Human Genome Project

Q36. What was the Human Genome Project?

Answer: The Human Genome Project was an international effort to sequence and map the entire human genome.

Q37. Approximately how many genes are present in humans?

Answer: Humans have approximately 30,000 genes.

Q38. What percentage of human DNA is identical among individuals?

Answer: About 99.9% of human DNA is identical among all individuals.

Q39. Name one application of Human Genome Project.

Answer: It helps in disease diagnosis, gene therapy, and development of personalised medicine.

Q40. What is bioinformatics?

Answer: Bioinformatics is the application of computer technology to store, analyse, and interpret biological data.

Section I: DNA Fingerprinting

Q41. What is DNA fingerprinting?

Answer: DNA fingerprinting is a technique to identify individuals based on unique patterns in their DNA.

Q42. On which DNA regions is fingerprinting based?

Answer: DNA fingerprinting is based on polymorphism in repetitive DNA sequences such as VNTRs.

Q43. Who developed DNA fingerprinting technique?

Answer: DNA fingerprinting was developed by Alec Jeffreys.

Q44. Name one application of DNA fingerprinting.

Answer: DNA fingerprinting is used in forensic investigations and paternity testing.

Q45. Why is DNA fingerprinting unique for each individual?

Answer: Because the number and arrangement of repetitive DNA sequences vary among individuals.

Section J: Integrated Concepts

Q46. What is central dogma of molecular biology?

Answer: Central dogma explains the flow of genetic information from DNA to RNA to protein.

Q47. Why is transcription essential for translation?

Answer: Transcription produces mRNA, which carries genetic information from DNA to ribosomes for protein synthesis.

Q48. What is the role of primase in replication?

Answer: Primase synthesises RNA primers required for initiation of DNA synthesis.

Q49. Why is RNA polymerase different from DNA polymerase?

Answer: RNA polymerase does not require a primer and synthesises RNA instead of DNA.

Q50. Why is regulation of gene expression important?

Answer: It prevents unnecessary protein synthesis and ensures cellular efficiency and proper development.