Lecture on Mendelian Genetics

Introduction

• Study of chemistry, biochemistry, and biology helps understand molecular and cellular processes in life.
• Heredity: concept understood long before cells and molecules were known.
• Children resemble their parents; traits (hair color, skin tone, height) are passed through generations.

Gregor Mendel and the Inception of Genetics

• Mendel: pivotal figure in genetics, born in a poor agricultural area of Europe.
• Entered an Augustinian monastery at 21, later studied science in Vienna.
• Proposed heredity is based on discrete units called genes.

Mendel's Work with Pea Plants

• Pea plants chosen for visible traits, short generations, and controllable mating.
• Used hybridization to study inheritance: crossed true-breeding plants (parental generation) to observe F1 and F2 generations.

Mendel's Experiments and Findings

• Law of Segregation:

  • Observed purple (dominant) vs. white (recessive) flowers after hybridization.
  • F1 generation: all purple (dominant trait).
  • F2 generation: 3:1 ratio of purple to white flowers, supporting gene theory.
  • Introduced concepts of dominant and recessive traits, alleles, homozygous, and heterozygous.
  • Punnett squares used to predict genetic outcomes.

• Law of Independent Assortment:

  • Explored dihybrid crosses (two traits at once, e.g., seed color and shape).
  • F1 generation: heterozygous for both traits, dominant phenotype expressed.
  • F2 generation: 9:3:3:1 phenotypic ratio.

Extensions and Limitations of Mendelian Genetics

• Not all inheritance patterns are simple.
• Incomplete Dominance: third, intermediate phenotype (e.g., pink snapdragons from red and white parents).
• Codominance: both phenotypes expressed simultaneously.
• Advanced understanding requires knowledge of chromosomes.