Polygenic Inheritance:
* Multiple genes: Involves multiple genes contributing to a single trait.
* Additive effect: Each gene contributes a small, incremental effect to the overall phenotype.
* Continuous variation: Results in a continuous distribution of phenotypes, often resembling a bell curve.
* Example: Human height, skin color, hair color.
Incomplete Dominance:
* Two alleles: Involves two alleles for a single gene, with neither being completely dominant.
* Intermediate phenotype: The heterozygote expresses a phenotype intermediate between the two homozygous phenotypes.
* Discrete variation: Results in discrete phenotypes, not a continuous spectrum.
* Example: Snapdragon flower color (red x white = pink).
Key Differences:
| Feature | Polygenic Inheritance | Incomplete Dominance |
|---|---|---|
| Number of genes involved | Multiple genes | Single gene with two alleles |
| Interaction of alleles | Additive effects of multiple genes | Neither allele is fully dominant |
| Phenotype of heterozygote | Intermediate phenotype, but within a continuous range | Distinct intermediate phenotype |
| Variation in phenotype | Continuous distribution | Discrete phenotypes |
In summary:
* Polygenic inheritance is like mixing paints, where multiple colors contribute to a blended result.
* Incomplete dominance is like mixing red and white paint to create pink, a distinct color that isn't fully red or fully white.
