Molecular Basis of Inheritance : best Handwritten notes class 12

Molecular Basis of Inheritance : best Handwritten notes class 12

🔹 1. DNA as Genetic Material

• Griffith’s Experiment (1928): Transformation principle.
• Avery, MacLeod, McCarty (1944): DNA is genetic material.
• Hershey & Chase (1952): Confirmed DNA as genetic material using bacteriophages.

🔹 2. Structure of DNA

• Watson and Crick (1953): Double helix model.
• DNA has:
  • Sugar–phosphate backbone
  • Nitrogenous bases: A–T (2 H bonds), G–C (3 H bonds).
• Antiparallel strands (5’ → 3’ and 3’ → 5’).
• Chargaff’s rule: A = T, G = C.

🔹 3. Packaging of DNA

• DNA wraps around histone proteins to form nucleosomes (“beads on a string”).
• Further coiling → chromatin → chromosomes.
• Euchromatin: Light, active.
• Heterochromatin: Dark, inactive.

🔹 4. Replication of DNA

• Semi-conservative model proved by Meselson & Stahl (1958).
• Enzymes involved:
  • DNA helicase → unwinds
  • DNA polymerase → adds nucleotides
  • DNA ligase → joins Okazaki fragments
• Leading strand (continuous) & lagging strand (discontinuous).

🔹 5. Transcription (DNA → RNA)

• Enzyme: RNA polymerase
• In Prokaryotes: mRNA is polycistronic, no splicing.
• In Eukaryotes:
  • Pre-mRNA undergoes:
    • Capping (5′ cap)
    • Tailing (Poly-A tail at 3′ end)
    • Splicing (removal of introns)

🔹 6. Genetic Code

• Triplet codons (64 codons for 20 amino acids).
• Features:
  • Universal, Degenerate, Non-overlapping.
• Start codon: AUG (Methionine).
• Stop codons: UAA, UAG, UGA.

🔹 7. Translation (Protein Synthesis)

• Occurs in ribosomes.
• Steps:
  1. Initiation (mRNA binds to ribosome)
  2. Elongation (tRNA brings amino acids)
  3. Termination (stop codon, polypeptide released)

🔹 8. Regulation of Gene Expression

• Prokaryotes: Lac operon model (Jacob & Monod).
  • Inducible operon; lactose acts as inducer.
• Eukaryotes: More complex; transcription factors regulate.

🔹 9. Human Genome Project (HGP)

• Completed in 2003.
• Goals: Identify all genes, sequence DNA.
• Findings:
  • Humans have ~20,000–25,000 genes.
  • <2% of genome codes for proteins.

🔹 10. DNA Fingerprinting

• Based on VNTRs (Variable Number Tandem Repeats).
• Uses: Forensics, paternity testing, genetic disorders.
• Technique developed by Alec Jeffreys (1985).

Molecular Basis of Inheritance Pdf

Molecular Basis of Inheritance Pdf