Lecture Notes: Gregor Mendel and the Fundamentals of Genetics

Introduction

• Setting: 1800s, a quiet monastery garden.
• Key Figure: Gregor Mendel, Austrian monk, known as the father of genetics.
• Focus: Study of pea plants to understand heredity.

Mendel's Experiments with Pea Plants

• Observations: Characteristics such as height, seed shape, seed color, flower color.
• Experimentation: Cross-pollination of plants with different traits.
  • Example Questions:
    • What happens when crossing tall with short plants?
    • What happens when crossing yellow-seeded with green-seeded plants?

Findings

F1 Generation

• Contrary to beliefs of the time, offspring traits did not blend.
• Observed disappearance of certain traits (e.g., all tall plants, all yellow peas).

F2 Generation

• Hidden traits reappeared but in specific ratios (3:1).
  • 3 out of 4 plants were tall, 1 out of 4 was short.
  • Similar ratio for seed color.

Mendel's Laws of Heredity

1. Law of Segregation

• Genes exist in multiple forms known as alleles.
• Example: Seed color
  • Alleles: Capital Y for yellow, lowercase y for green.
• Alleles segregate during gamete formation; offspring get one allele from each parent during fertilization.

2. Law of Dominance

• Alleles can be dominant or recessive.
  • Dominant alleles mask recessive alleles.
  • Example: Purple (dominant) vs. white flowers (recessive).

3. Law of Independent Assortment

• Different traits are inherited independently.
  • Analogy: Choice of entree doesn't affect choice of dessert.
  • A plant's height is independent of seed color or flower color.

Conclusion

• Mendel's work laid the foundation for understanding heredity.
• Current genetics is more complex but his laws remain fundamental.
• Future topics: Application to humans, genetic disorders, exceptions to Mendel's laws.

Closing

• Presenter: Leslie Samuel from Interactive Biology.
• Goal: Make biology engaging and fun.
• Next Steps: Continue exploring genetics.