MOLECULAR BASIS OF INHERITANCE -1- Over the next hundred years, the nature of the putative genetic material was investigated culminating in the realisation that DNA – deoxyribonucleic acid – is the genetic material, at least for the majority of organisms.

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Master Table: Molecular Basis of Inheritance

Topic	Explanation	Key Details	MCQ
Inheritance Patterns	Factors regulating inheritance patterns were unclear in Mendel’s time but are now linked to genetic material (DNA/RNA).	– DNA is the genetic material in most organisms. – RNA functions as a genetic material in some viruses and a messenger in others.	Q: What is the genetic material in most organisms? A) DNA B) RNA C) Proteins D) Lipids. Ans: A
Introduction to DNA & RNA	Nucleic acids are polymers of nucleotides, forming DNA and RNA. DNA is genetic material in most organisms, while RNA has roles as adapter, structural, and catalytic molecules.	– DNA: Deoxyribonucleic acid. – RNA: Ribonucleic acid. – Functions: Genetic material, catalysis, and protein synthesis.	Q: Which nucleic acid acts primarily as genetic material? A) DNA B) RNA C) Both equally D) Proteins. Ans: A
Structure of DNA	DNA is a polymer of deoxyribonucleotides; its length is measured in base pairs (bp).	– Examples: φ ×174 (5386 nucleotides), E. coli (4.6 × 10⁶ bp), Human haploid DNA (3.3 × 10⁹ bp).	Q: What is the haploid DNA content of humans? A) 1.5×10⁹ bp B) 4.6×10⁶ bp C) 3.3×10⁹ bp D) 5×10⁹ bp. Ans: C
Structure of Polynucleotide Chain	A polynucleotide chain consists of nucleotides linked via phosphodiester bonds, forming a sugar-phosphate backbone.	– Nitrogenous bases: Purines (A, G) and Pyrimidines (C, T/U). – Nucleotides linked by 3’-5’ phosphodiester bonds.	Q: Which bond links nucleotides in a polynucleotide chain? A) Phosphodiester B) Hydrogen C) Peptide D) Glycosidic. Ans: A
Discovery of DNA	DNA was first identified as ‘Nuclein’ by Friedrich Meischer in 1869.	– Meischer: DNA as an acidic substance in the nucleus. – Structure elucidated by Watson, Crick, Wilkins, and Franklin in 1953.	Q: Who first identified DNA as a substance? A) Meischer B) Watson C) Franklin D) Chargaff. Ans: A
Chargaff’s Rules	The ratios of A:T and G:C are constant and equal to 1 in double-stranded DNA.	– A pairs with T (2 H-bonds). – G pairs with C (3 H-bonds).	Q: If G = 30%, what is the proportion of A? A) 20% B) 40% C) 30% D) 10%. Ans: A
Watson and Crick’s Model	Proposed the DNA double-helix structure based on Franklin and Wilkins’ X-ray diffraction data.	– Anti-parallel strands. – Complementary base pairing (A-T, G-C).	Q: What is the shape of DNA as described by Watson and Crick? A) Double helix B) Linear C) Circular D) Branched. Ans: A
Salient Features of DNA Double-Helix	Key structural and functional features of DNA that define its role as genetic material.	– Two polynucleotide chains with sugar-phosphate backbone. – Anti-parallel polarity (5’ → 3’ and 3’ → 5’). – A-T (2 H-bonds); G-C (3 H-bonds). – Right-handed coil, 3.4 nm pitch, ~10 bp per turn. – Base stacking adds stability.	Q: What is the pitch of the DNA helix? A) 3.0 nm B) 3.4 nm C) 10 nm D) 0.34 nm. Ans: B
DNA Replication	Semi-conservative process; parental strands template for daughter DNA synthesis.	Identical DNA copies ensure genetic continuity.	Q: DNA replication is: A) Semi-conservative B) Conservative C) Dispersive D) Redundant. Ans: A
RNA vs. DNA	RNA contains ribose and uracil; DNA has deoxyribose and thymine.	RNA: Single-stranded, catalytic. DNA: Double-stranded, genetic material.	Q: What sugar is present in RNA? A) Ribose B) Deoxyribose C) Fructose D) Glucose. Ans: A
Human Genome Project	Sequencing the entire human genome has revolutionized genomics.	~20,000-25,000 genes identified; applications in medicine, evolution, and agriculture.	Q: The Human Genome Project identified approximately how many genes? A) 10,000 B) 50,000 C) 25,000 D) 1,000. Ans: C
Why RNA is an Adapter	RNA bridges genetic information (mRNA) to protein synthesis via tRNA, transferring amino acids to the ribosome.	RNA acts as a messenger, adapter, structural, and catalytic molecule.	Q: Which RNA is an adapter molecule? A) mRNA B) tRNA C) rRNA D) snRNA. Ans: B
RNA as a Catalyst	Ribozymes (catalytic RNAs) catalyze reactions such as splicing and peptide bond formation.	Example: Peptidyl transferase activity of rRNA during translation.	Q: Which process involves RNA catalysis? A) DNA replication B) RNA splicing C) Translation D) None. Ans: C
N-Nucleosidic Linkage	Bonds between nitrogenous bases and sugars in nucleotides; differs from glycosidic bonds (sugar-sugar bonds).	– N-glycosidic linkage: Sugar (C1) + Base (N). – Glycosidic linkage: Sugar + Sugar.	Q: What links nitrogenous bases to sugars in nucleotides? A) Phosphodiester B) N-glycosidic C) Peptide D) H-bonds. Ans: B
Wilkins and Franklin’s Role	Produced X-ray diffraction data crucial for Watson-Crick’s DNA structure model.	Franklin: Helical DNA structure. Wilkins: Crystallography techniques.	Q: Who provided X-ray diffraction data for DNA structure? A) Watson B) Franklin C) Chargaff D) Mendel. Ans: B
Meischer’s Contribution	Isolated DNA (then called “nuclein”) from pus cells in 1869, marking the discovery of genetic material.	DNA was acidic and present in nuclei.	Q: Who first discovered DNA? A) Meischer B) Watson C) Wilkins D) Chargaff. Ans: A