gen-define-polygenic-traits-and-give-one-short-worked-example-7922

Define polygenic traits and give one short worked example.

# Polygenic Traits **Definition:** Polygenic traits are characteristics controlled by **two or more genes**, each contributing to the phenotype in an additive manner. These traits typically show **continuous variation** rather than distinct categories. ## Worked Example: Human Skin Color **Scenario:** Assume skin color is controlled by 2 genes (A and B), each with two alleles: - Dominant alleles (A, B) add pigment - Recessive alleles (a, b) add no pigment **Cross:** AaBb × AaBb (two medium-toned parents) **Offspring phenotypes based on "capital letter" count:** | Capital Letters | Genotype Examples | Phenotype | Ratio | |----------------|-------------------|-----------|-------| | 4 | AABB | Very dark | 1/16 | | 3 | AABb, AaBB | Dark | 4/16 | | 2 | AaBb, AAbb, aaBB | Medium | 6/16 | | 1 | Aabb, aaBb | Light | 4/16 | | 0 | aabb | Very light | 1/16 | **Result:** A **1:4:6:4:1 ratio** showing continuous variation from very light to very dark skin, rather than simple dominant/recessive categories. *Note: Actual human skin color involves 3+ genes, creating even more variation.*