Overview
This lecture explains the difference between incomplete dominance and codominance in genetics, with real-life examples for each concept.
Mendel’s Genetics Basics
- Gregor Mendel is known as the father of genetics for his pea plant experiments.
- Classic Mendel traits had two alleles: one dominant and one recessive, one would mask the other.
Incomplete Dominance
- Incomplete dominance occurs when crossing two individuals with different phenotypes produces an intermediate, blended phenotype.
- The resulting offspring display a third phenotype that is a mix of the two parent traits.
- Example: Red and white snapdragon flowers produce pink flowers.
- Example: Crossing a white and black animal produces a greyish-blue offspring.
- Analogy: Mixing paints (red + white = pink).
Codominance
- Codominance happens when both parent traits appear together in the offspring without blending.
- Both alleles are equally expressed in the phenotype.
- Example: Crossing a white cow and a brown cow results in a spotted cow with both colors.
- Example: A speckled chicken has both black and white feathers.
- Example: 4 o'clock plants show both alleles together in the appearance.
Key Terms & Definitions
- Phenotype — the observable traits or characteristics of an organism.
- Allele — a variant form of a gene.
- Incomplete dominance — a genetic situation where neither allele is completely dominant, resulting in a blended phenotype.
- Codominance — a genetic scenario where both alleles are fully expressed, producing offspring with both traits visible.
Action Items / Next Steps
- Review textbook sections on incomplete dominance and codominance.
- Practice identifying examples of each type in homework problems.