Overview
This lecture introduces Gregor Mendel’s foundational experiments with pea plants and explains his three key laws of heredity: segregation, dominance, and independent assortment.
Gregor Mendel’s Experiments
- Gregor Mendel observed and experimented with pea plant traits like height, seed shape, and color in the 1800s.
- He cross-pollinated plants with contrasting traits and tracked their offspring.
- The first generation (F1) showed only one trait; the other seemed to disappear.
- When F1 plants were crossed, the hidden traits reappeared in the second generation (F2) in a 3:1 ratio.
Mendel’s Laws of Heredity
Law of Segregation
- Genes exist in different forms called alleles.
- Each parent contributes one allele for each trait to offspring.
- Alleles separate (segregate) during gamete (sex cell) formation and reunite at fertilization.
Law of Dominance
- Some alleles are dominant and can mask the effect of recessive alleles.
- In a plant with one dominant and one recessive allele, only the dominant trait appears.
Law of Independent Assortment
- Genes for different traits are inherited independently of each other.
- The inheritance of one trait does not affect the inheritance of another.
Key Terms & Definitions
- Gene — a unit of heredity that determines a trait.
- Allele — different forms of a gene (e.g., Y for yellow, y for green).
- Gamete — a sex cell (egg or sperm) carrying one allele for each trait.
- Dominant allele — an allele that masks the presence of a recessive allele.
- Recessive allele — an allele whose effect is hidden when paired with a dominant allele.
Action Items / Next Steps
- Prepare for the next lecture on applications of Mendel’s laws to humans and genetic disorders.
- Review definitions and examples of Mendel’s three laws.
- Note that future lessons will cover exceptions to Mendel’s laws.