A phenocopy is a trait found in an organism that develops as a result of environmental factors and which approximates an identical or similar trait in another organism in which that trait is present due to genetic factors. The word is also use to describe a trait that results from environmental factors that is not found in other individuals of the same species. A phenocopy is, therefore, part of an organism's phenotype, which consists of its entire observable set of traits. An organism's genotype is its entire genetic code, contained in its DNA, and includes all possible traits and characteristics, not just those that are expressed in a given individual.
The study of evolution and the development of species is closely tied to genetics and heredity. Recognizing a particular trait in an organism as a phenocopy, as opposed to an inherited trait that is encoded in its genotype, is important when trying to classify organisms or to trace their development over time. Often a phenocopy is mistaken for a genetic trait, leading to confusion in classification or identification.
A human being whose hair has become lighter in shade due to prolonged exposure to bright sunlight, as opposed to another whose hair is naturally that color, is one example of the difference between a phenocopy and a genetic trait. An animal whose coat changes color with changes in temperature is another example. Snowshoe hares, for instance, have a coat that becomes white during the winter but reverts to mottled brown and grey shades during the summer. Examples of phenocopy traits are most commonly observed in an organism's appearance but may also be exhibited in the organism's behavior.
Another way to define a phenocopy is by the trait's ability to be passed down to the organism's descendants. The snowshoe hare's offspring for example, would retain their gray-brown coloring if they were not exposed to winter conditions. The white coloration is not inherited but is influenced by the animal's environment. Size is another example of an expression of a phenocopy. An animal that lives in a food rich environment may grow to the limits of size for its species while its offspring may fail to reach a similar size in an environment where food is scarce.