Distinguish between pleiotropy and polygenic inheritance, giving one example of each.

1. 1 · Define pleiotropy. One gene with several phenotypic effects, usually through a metabolic pathway.
2. 2 · Give its example. Phenylketonuria: a faulty phenylalanine hydroxylase gene causes mental retardation and less hair and skin pigment.
3. 3 · Define polygenic inheritance. One trait controlled by three or more genes whose effects add up.
4. 4 · Give its example. Skin colour: AABBCC darkest, aabbcc lightest, AaBbCc intermediate; the environment also acts.
5. 5 · Link to real life. Height is polygenic, so good childhood nutrition helps a child reach their full height.
6. 6 · Close in one line. So pleiotropy is one gene with many effects; polygenic inheritance is many genes for one effect.

Scoring tip: A two-column table (feature, pleiotropy, polygenic) makes a neat 3-mark answer.