Concise Notes on Mendelian Inheritance

Gregor Mendel

  • Known as the "Father of Genetics" (1822-1884).
  • Conducted experiments on pea plants to study inheritance of traits.

Mendel's Pea Plant Experiments

  • Produced pure strains by self-pollination for generations.
  • Cross-bred plants to create hybrids.

Definitions

  • Pure Strains/True Breeding Plants: Produce offspring with the same trait as the parent.
  • Hybrid: Offspring from two different true-breeding parents.

Eight Pea Plant Traits

  • Seed Shape: Round (R) or Wrinkled (r)
  • Seed Color: Yellow (Y) or Green (y)
  • Pod Shape: Smooth (S) or Wrinkled (s)
  • Pod Color: Green (G) or Yellow (g)
  • Seed Coat Color: Gray (G) or White (g)
  • Flower Position: Axial (A) or Terminal (a)
  • Plant Height: Tall (T) or Short (t)
  • Flower Color: Purple (P) or White (p)

Mendel's Conclusions

  1. Traits are passed by discrete units called 'factors' (now known as genes).
  2. Each organism carries two genes for each trait, one from each parent.
  3. Only one gene from each parent is passed on to offspring (haploid).

Mendel's Laws

  1. Law of Dominance: In a cross of pure contrasting traits, only one trait appears in offspring.
  2. Law of Segregation: Each parent passes one of their two alleles for each gene to offspring.
  3. Law of Independent Assortment: Alleles for different traits are distributed independently.

Genotype vs. Phenotype

  • Genotype: Genetic makeup (e.g., AA, Aa, aa).
  • Phenotype: Outward appearance (e.g., Dark or Light).
  • Alleles: Two forms of a gene; dominant (capital letter) and recessive (lowercase letter).

Genetic Crosses

  • Monohybrid Cross: Involves one trait (e.g., flower color).
  • Dihybrid Cross: Involves two traits (e.g., flower color and plant height).

Punnett Square

  • A diagram to summarize possible genetic combinations. Used for predicting offspring traits.

Test Cross

  • Used to determine the genotype of a dominant trait individual by crossing it with a homozygous recessive.
  • Outcomes: 100% dominant trait indicates homozygous dominant (PP); mixed traits indicate heterozygous (Pp).