Phenocopy

A phenocopy is an individual whose phenotype (generally referring to a single trait), under a particular environmental condition, is identical to the one of another individual whose phenotype is determined by the genotype. In other words the phenocopy environmental condition mimics the phenotype produced by a gene.

The term was coined by Richard Goldschmidt in 1935. He used it to refer to forms, produced by some experimental procedure, whose appearance duplicates or copies the phenotype of some mutant or combination of mutants.

A phenocopy is not a type of mutation, it is an environmentally induced, non-hereditary phenotypic modification that resembles a similar phenotype produced by a gene mutation (genocopy).

An example of a phenocopy are the Vanessa genus of butterflies who can change phenotype based on the local temperature. If introduced to Lapland they mimic butterflies localised to this area and if localised to Syria they mimic butterflies of this area. These phenotypes aren't inherited and are solely due to environment.

Another great example is in Drosophila melanogaster. A variety of environmental factors produce abnormalities in these fruit flies that resemble the abnormal phenotypes of known genetic mutations. The environmental agents producing phenocopies includes temperature, shock, radiation, and various chemical compounds. In fruit fly, Drosophila melanogaster, the normal body colour is brownish-gray with black margins. A hereditary mutant for this was discovered by T.H. Morgan in 1910 where the body colour is yellow. This was a genotypic character which was constant in both the flies in all environments. However, in 1939, Rapport discovered that if larva of normal flies were fed with silver salts, they develop into yellow bodied flies irrespective of their genotype. The yellow bodied flies which are genetically brown is a variant of the original yellow bodied fly. This is now called a phenocopy.

Phenocopy can also be observed in Himalayan rabbits. Himalayan rabbits are white in colour with black tail, nose, and ears. When raised in moderate temperatures they grow up to be phenotypically similar to genetically Black rabbits. However when raised in colder climates, they become phenotypically distinguishable. The Himalayan rabbits show black colouration of their coats, resembling the genetically black rabbits. Hence this Himalayan rabbit is a phenocopy of the genetically black rabbit.

An incorrect example of a phenocopy is a person with bleached brunette hair; the bleached hair is intended to mimic genetically determined blonde hair of actual blonde people. The false phenocopy can be easily distinguished by observing the roots of the hair or by shining an ultraviolet light on the bleached brunette hair.

A correct example of a phenocopy is a person whose anti-psychotic medication causes them to manifest the same symptoms as the genetically determined Parkinsons disease.