Molecular Basis of Inheritance

32 solved questions from Class 12 Biology, each with the full working. Tap any question to see the step-by-step solution.

• 1 What is the primary topic or theoretical principle explored in 'Molecular Basis of Inheritance' (Class 12 BIOLOGY)? medium MCQ Chapter Core Principle
• 2 Which key mechanism or analytical rule is highlighted in 'Molecular Basis of Inheritance'? medium MCQ Key Analytical Mechanism
• 3 What is the primary topic or principle explained in 'Molecular Basis of Inheritance' (Class 12 Biology)? medium MCQ Chapter Core Concept
• 4 Which key observation or fact is central to understanding 'Molecular Basis of Inheritance'? medium MCQ Key Fact & Mechanism
• 5 Why is the study of 'Molecular Basis of Inheritance' important for students of Class 12? medium MCQ Learning Significance
• 6 What is a common application or real-world example related to 'Molecular Basis of Inheritance'? medium MCQ Real World Application
• 7 What key takeaway should students retain after completing 'Molecular Basis of Inheritance'? medium MCQ Chapter Summary & Takeaway
• 8 A point mutation changes the codon UGC (cysteine) to UAA (stop codon) in the mRNA of a human beta‑globin gene. Discuss the molecular consequences of this nonsense mutation on the synthesized hemoglobin protein and its possible phenotypic effect in an individual. hard 5 marks Effect of nonsense mutations
• 9 Explain how the CRISPR‑Cas9 system introduces a site‑specific double‑strand break in a target DNA sequence. medium 2 marks CRISPR‑Cas9 mechanism
• 10 Which type of point mutation results in a codon that still codes for the same amino acid? easy MCQ 1 mark Types of point mutations
• 11 In a genetic cross of two heterozygous pea plants (Tt × Tt) where the gene T for tallness is located on a chromosome that undergoes 2 crossover events between the T locus and a nearby gene D for disease resistance, what is the probability that a gamete carries the dominant allele T and the recessive allele d? hard 4 marks Recombination and crossover effects
• 12 Briefly explain the specific function of DNA ligase in the construction of recombinant plasmids. medium 2 marks Role of DNA ligase in recombinant DNA
• 13 Describe the Sanger chain‑termination method of DNA sequencing and explain how the incorporation of dideoxynucleotides allows the sequence to be read. hard 5 marks Sanger DNA sequencing principle
• 14 Which of the following correctly describes the hydrogen‑bonding pattern in double‑stranded DNA? easy MCQ 1 mark Base‑pairing in DNA
• 15 In a PCR experiment, a 500 bp target is amplified starting with 1 copy of template DNA. If the efficiency of each cycle is 90 % (i.e., each cycle produces 0.9 new copies per existing copy), how many copies will be present after 30 cycles? Express your answer as a whole number of copies. hard 3 marks Quantitative PCR amplification
• 16 A point mutation changes the codon GAA (glutamic acid) to GAG (glutamic acid) in the mRNA of a gene coding for an enzyme. Explain why this mutation is silent and discuss its possible impact if it occurs in a highly conserved region of the protein. hard 4 marks Silent mutation consequences
• 17 Outline how the CRISPR‑Cas9 system can be used to correct a point mutation in a patient’s diseased cell. Include the roles of guide RNA, Cas9, a repair template, and the cellular repair pathway involved. hard 5 marks CRISPR gene editing mechanism
• 18 What is the main difference between DNA and RNA molecules in terms of their sugar and base composition? easy 1 mark DNA vs RNA structure
• 19 During PCR, a 250‑bp fragment is amplified from a single copy template. If each cycle increases the number of copies by 80 % (i.e., each existing copy produces 0.8 additional copies), how many copies will be present after 25 cycles? Round to the nearest whole number. medium 2 marks PCR amplification kinetics
• 20 A missense mutation changes the codon GCC (alanine) to GAC (aspartic acid). If this mutation occurs in the active site of an enzyme, predict its impact on the enzyme’s tertiary structure and catalytic activity. hard 4 marks Missense mutation effect on enzyme structure
• 21 A point mutation changes the mRNA codon AAA (lysine) to AAG (lysine). Explain why this mutation is silent and describe how wobble pairing allows the same amino acid to be coded. medium 2 marks Silent mutation & wobble pairing
• 22 Which nitrogenous base is present only in RNA and not in DNA? easy 1 mark RNA‑DNA base difference
• 23 During PCR, each cycle amplifies existing DNA by 75 % (i.e., each existing copy produces 0.75 additional copies). Starting from a single copy of template DNA, how many copies will be present after 30 cycles? Round to the nearest whole number. hard 3 marks PCR exponential amplification
• 24 In a PCR reaction, 10 copies of a 200‑bp DNA fragment are amplified with an efficiency of 70 % per cycle. After 20 cycles, approximately how many copies are present? Round to the nearest whole number. medium 2 marks PCR efficiency calculation
• 25 During DNA replication, how does the 3'→5' exonuclease activity of DNA polymerase contribute to replication fidelity? easy 1 mark DNA replication proofreading
• 26 A nonsense mutation at codon 150 of the β‑globin gene introduces a premature stop codon (UAA). Explain how this mutation affects β‑globin mRNA stability, protein synthesis, and the clinical phenotype seen in β‑thalassemia major. hard 5 marks Nonsense mutation consequences
• 27 A cystic fibrosis patient has a G→A nonsense mutation in the CFTR gene that creates a premature stop codon at position 508. Design a CRISPR‑Cas9 strategy to correct this point mutation, specifying the roles of guide RNA, Cas9, repair template, and the cellular repair pathway involved. hard 4 marks CRISPR‑Cas9 gene editing
• 28 To correct a G→A point mutation that creates a premature stop codon in exon 3 of the human DMD gene, which of the following CRISPR‑Cas9 strategies will most likely achieve precise correction in patient‑derived myoblasts? hard MCQ 5 marks CRISPR‑Cas9 HDR gene correction
• 29 A missense mutation changes the codon CGU (arginine) to CGU (still arginine) in a region of a protein that is highly conserved and forms part of the active site. Discuss how this seemingly conservative change can still affect the protein’s tertiary structure and catalytic activity, considering hydrogen‑bonding, side‑chain interactions, and enzyme kinetics. hard 4 marks Effect of missense mutation on protein function
• 30 In a PCR experiment, the reaction starts with 5 copies of a 300‑bp DNA fragment. Each cycle has an amplification efficiency of 85 % (i.e., each existing copy produces 0.85 new copies). How many copies are present after 15 cycles? Round to the nearest whole number. medium 2 marks PCR amplification calculation
• 31 Which nitrogenous base is present only in RNA and not in DNA? easy MCQ 1 mark RNA‑specific base
• 32 In the coding sequence of a gene, a cytosine at position 237 is replaced by a thymine. The original codon was GCG coding for alanine. Which of the following is the resulting codon and the type of mutation? easy MCQ 1 mark Point mutation classification