Mendelian Genetics

Introduction to Genetics

• Genetics is the study of heredity and the variation of inherited characteristics.
• Understanding genetics was possible before the discovery of cells and molecules.
• Gregor Mendel is a key figure in the history of genetics.

Gregor Mendel

• Born in a poor agricultural area in Europe.
• Joined an Augustinian monastery and later studied science in Vienna.
• Returned to the monastery to conduct his research on heredity.

Mendel’s Experiments

• Focused on pea plants due to varying traits and short generations.
• Controlled plant mating by cross-fertilization.
• True-breeding plants: Plants that consistently produce offspring with specific traits.
• Hybridization: Cross-breeding of two true-breeding plants.
  • Parental generation (P): True-breeding plants.
  • F1 generation: First filial generation.
  • F2 generation: Second filial generation.

Key Findings

• Developed the gene theory: Traits are passed via discrete units known as genes.
• Two fundamental laws:
  1. Law of Segregation
     • Each organism carries two alleles for each trait.
     • During reproduction, alleles segregate so each gamete carries one allele.
  2. Law of Independent Assortment
     • Genes for different traits can segregate independently during gamete formation.

Experiment Example

• Crossed purple and white flowering plants.
• F1 generation was entirely purple.
• F2 generation had a 3:1 ratio of purple to white.
• Dominant and recessive traits: Purple is dominant; white is recessive.

Genetics Terminology

• Phenotype: Observable physical traits.
• Genotype: Genetic makeup of an organism.
• Homozygous: Identical alleles for a trait.
• Heterozygous: Different alleles for a trait.

Advanced Genetic Concepts

• Incomplete Dominance: Intermediate phenotype in heterozygotes (e.g., pink snapdragons from red and white).
• Codominance: Both alleles in heterozygotes are expressed (e.g., blood type).
• Complex inheritance patterns beyond Mendel’s basic principles.

Importance of Mendel's Work

• Laid the foundation for modern genetics.
• His laws help predict genetic outcomes using probability.

Mendel's work demonstrated the mathematical reliability behind inheritance, utilizing concepts such as Punnett squares to predict genetic distributions. While not all inheritance patterns are simple, his principles remain fundamental to genetics. The understanding of chromosomes and genetic material has further expanded on his theories.