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Genetics & Molecular Biology

Mendelian genetics, DNA structure, replication, gene expression

Key Concepts
  • Mendel's 1st law: Law of Segregation — alleles separate during gamete formation
  • Mendel's 2nd law: Law of Independent Assortment — genes on different chromosomes assort independently
  • Dominant allele masks recessive in heterozygote
  • Codominance: both alleles expressed (e.g. ABO blood group type AB)
  • Sex-linked traits: carried on X chromosome; males (XY) are more often affected
Important Formulae
Hardy-Weinberg equation p² + 2pq + q² = 1; p + q = 1
Monohybrid cross (Aa × Aa) Phenotype ratio 3:1; genotype ratio 1:2:1
Dihybrid cross (AaBb × AaBb) Phenotype ratio 9:3:3:1
Quick Tips
  • Haemophilia and colour-blindness are X-linked recessive — more common in males.
  • Chromosomal disorders: Down's (trisomy 21), Turner's (45, X0), Klinefelter's (47, XXY).
  • Crossing over in prophase I of meiosis produces genetic recombination.
Sample Practice Questions

  1. Linkage is the tendency of genes on the same chromosome to:

    • Separate independently
    • Inherited together
    • Show dominance
    • Cause mutations
    Show answer

    Answer: Inherited together

  2. Chromosomal theory of inheritance was proposed by:

    • Darwin and Wallace
    • Sutton and Boveri
    • Watson and Crick
    • Mendel and Morgan
    Show answer

    Answer: Sutton and Boveri

  3. Mendel's law of segregation states that alleles:

    • Blend together in offspring
    • Separate during gamete formation
    • Always show dominance
    • Are always identical
    Show answer

    Answer: Separate during gamete formation

  4. Translation occurs at:

    • Nucleus
    • Mitochondria
    • Ribosome
    • Golgi apparatus
    Show answer

    Answer: Ribosome

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Practice Questions

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