A phenocopy is an individual whose phenotype
A phenotype is an organism's observable characteristics or traits: such as its morphology, development, biochemical or physiological properties, behavior, and products of behavior...

 (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
The genotype is the genetic makeup of a cell, an organism, or an individual usually with reference to a specific character under consideration...

. In other words the phenocopy environmental condition mimics the phenotype produced by a gene.

The term was coined by Richard Goldschmidt
Richard Goldschmidt
Richard Benedict Goldschmidt was a German-born American geneticist. He is considered the first to integrate genetics, development, and evolution. He pioneered understanding of reaction norms, genetic assimilation, dynamical genetics, sex determination, and heterochrony...

 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
Vanessa can refer to:* A member service officer at SOMB.* Vanessa , a female given name coined by Jonathan Swift, originally as a nickname for Esther Vanhomrigh* Vanessa , a genus of butterflies...

 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
Syria , officially the Syrian Arab Republic , is a country in Western Asia, bordering Lebanon and the Mediterranean Sea to the West, Turkey to the north, Iraq to the east, Jordan to the south, and Israel to the southwest....

 they mimic butterflies of this area. These phenotypes aren't inherited and are solely due to environment.

Another great example is in Drosophila melanogaster
Drosophila melanogaster
Drosophila melanogaster is a species of Diptera, or the order of flies, in the family Drosophilidae. The species is known generally as the common fruit fly or vinegar fly. Starting from Charles W...

. 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
Thomas Hunt Morgan
Thomas Hunt Morgan was an American evolutionary biologist, geneticist and embryologist and science author who won the Nobel Prize in Physiology or Medicine in 1933 for discoveries relating the role the chromosome plays in heredity.Morgan received his PhD from Johns Hopkins University in zoology...

 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.
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