Molecular Basis of Inheritance

Molecular Basis of Inheritance : best Handwritten notes class 12

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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

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Molecular Basis of Inheritance Pdf