The strength of environmental changes is sufficient to modify the effects of
many genes. In some instances, specific environmental changes may modify the
development of an organism so that its phenotype stimulates the effects of particular gene, although this effect is not inherited. Such individuals are known
Diabetics dependent on insulin are an example of a phenocopy of normal
individuals in the sense that drug environment prevents the effects of the
disease. Should their offspring also inherit diabetes? The phenocopy treatment
with insulin may have to be administered again to achieve the normal phenotype.
In no sense, therefore, is the diabetic changed by the insulin treatment. There
is only a phenotypic effect.
By subjecting normal Drosophila eggs, larvae, and pupae to various stress
conditions like temperature shock, we obtain a phenotype effect similar to that
of a mutant gene. The abnormal effects incurred through these agents are almost identical to specific gene mutations, although they are not inherited. Such individuals are known as phenocopies. The phenocopy partly imitates the mutant
An experiment on this problem was supported by Sang and McDonald
(1954), and it allows the exposure of 2 different stocks of Drosophila flies to the
phenocopy treatment. One is homozygous for wild type and the other is heterozygous
for wild type and the mutant recessive gene.
The mutant recessive, if it were homozygous, would produce a morphological
effect duplicated by the phenocopy. Therefore, after particular treatment, more
phenocopies are noted in the heterozygous stock than in the homozygous. This
may be considered as evidence that the phenocopy is controlling the developmental
The mutant effect will be partly duplicated by the phenocopy agent; sodium
meteorite is eyeless. Other effects that may also be noted in phenocopy are
changes in antennae and forelegs.
Prepare sufficient media for Drosophila growth and add around 0.1 mL of
silver nitrate to the 8 bottles and keep 2 bottles as control.
Transfer wild, colored Drosophilas into all 10 bottles. Permit the parents to lay
eggs for about 3 days and discard them. Later, examine the progeny. The silver
nitrate has the effect of phenocopy agent and changes the developing larvae to
colorless flies. This is not inherited.