A phenotype may be altered (compared to the original situation conditioned by its genotype) by nongenetic means. Examples: some hormones may cease to be secreted due to diseases, whereas the genes that determine their secretion remain intact; a person can go to a hairdresser and change the color of his/her hair; plastic surgery can be performed to alter the facial features of an individual; colored contact lenses may be worn; and a plant can grow beyond its genetically conditioned size through the application of phytohormones.
The effect of environmental influences on phenotypes can be observed in monozygotic twins who have grown up in different places. Generally, these twins present very distinct phenotypical features due to the environmental and cultural differences of the places where they lived and due to their different individual experiences in life.
(Biologically programmed phenotypical changes, such as nonpathological changes in skin color caused by sunlight exposure, tanning, or the variation of the color of some flowers depending on the pH of the soil cannot be considered independent from the genotype. In reality, these changes are planned by the genotype as natural adaptations to environmental changes.)