01Phenotypic plasticity
The same genotype can produce different phenotypes in different environments. Hydrangea flowers are blue in acidic soil and pink in alkaline soil. Himalayan rabbits and Siamese cats grow dark fur on cool extremities because a pigment enzyme only works at low temperature.
Sex of many reptiles (turtles) depends on egg incubation temperature.
02Humans
PKU (phenylketonuria) is genetic, but a low-phenylalanine diet prevents the symptoms. Height depends on genes and nutrition.
03Notebook box
Phenotype = genotype + environment.
Worked example: Identical twins raised apart differ in weight. What does that show? → Environmental factors affect phenotype even with identical genotypes.