Mendelian Genetics

Introduction to Genetics

• Heredity Concepts: Traits such as hair color, skin tone, and height are passed down from generation to generation.
• Historical Context: Before understanding cells and molecules, heredity was recognized but not understood.

Gregor Mendel's Contribution

• Background: Mendel joined an Augustinian monastery and later studied science in Vienna.
• Theory Development: Mendel proposed that heredity involves discrete units called genes.
• Research Methodology: Conducted experiments with pea plants to support gene theory.

Mendel's Experiments with Pea Plants

• Why Peas?

  • Varied visible traits such as flower color and seed shape.
  • Short generations and numerous offspring for data collection.
  • Controlled mating through removal of stamens.

• Hybridization Method

  • True-breeding plants: Produced the same traits in successive generations.
  • Parental Generation (P): True-breeding parent plants.
  • First Filial Generation (F1): Offspring of the P generation.
  • Second Filial Generation (F2): Offspring of the F1 generation.

Fundamental Laws of Genetics

• Law of Segregation

  • Each parent provides one allele for each trait.
  • F1 generation displayed only dominant traits.
  • F2 generation exhibited a 3:1 dominant to recessive trait ratio.
  • Explained through the concept of alleles, dominant and recessive traits.

• Law of Independent Assortment

  • Focuses on two traits simultaneously (dihybrid cross).
  • F1 generation is heterozygous for both traits.
  • Phenotypic ratio in F2 generation: 9:3:3:1.
  • Traits are inherited independently and alleles assort randomly.

Understanding Alleles and Genotypes

• Alleles: Different versions of a gene.
• Homozygous vs. Heterozygous:
  • Homozygous: Identical alleles for a trait.
  • Heterozygous: Different alleles for a trait.
• Genotype and Phenotype:
  • Multiple genotypes can produce the same phenotype.
  • Punnett squares used to predict allele combinations.

Extensions of Mendelian Genetics

• Incomplete Dominance

  • Example: Pink snapdragons from red and white parents.
  • Intermediate phenotypes appear in F1 generation.

• Codominance

  • Simultaneous expression of different phenotypes.

Beyond Mendelian Genetics

• Advanced Understanding
  • Not all inheritance follows Mendelian patterns.
  • Some genes have more than two alleles or produce multiple phenotypes.
  • Knowledge of chromosomes was needed for further advancements in genetics.