Pleiotropy:
* Focus: A single gene influencing multiple traits.
* Mechanism: The gene product (protein) can have multiple functions or affect different pathways, leading to various phenotypic effects.
* Example: Cystic fibrosis: One gene mutation affects multiple systems (lungs, pancreas, etc.)
Polygenic Inheritance:
* Focus: Multiple genes contributing to a single trait.
* Mechanism: Each gene has a small additive effect on the trait, resulting in a continuous distribution of phenotypes.
* Example: Height: Many genes influence height, resulting in a wide range of heights in a population.
Key differences:
| Feature | Pleiotropy | Polygenic Inheritance |
|---|---|---|
| Number of genes involved | One | Multiple |
| Number of traits affected | Multiple | One |
| Phenotype distribution | Often discrete (e.g., presence/absence of trait) | Continuous (e.g., height, skin color) |
| Example | Cystic fibrosis | Height, skin color |
Think of it this way:
* Pleiotropy: Imagine a single switch that controls multiple lights in a house.
* Polygenic Inheritance: Imagine multiple light bulbs contributing to the overall brightness of a room.
In summary:
* Pleiotropy: One gene, many effects.
* Polygenic Inheritance: Many genes, one effect.
