Control Mechanisms of Polyphenic Development in Insects

Abstract

It is well known that there is no necessary one-to-one relationship between the genetic makeup of an organism—its genotype—and the various characters and properties that constitute its phenotype. In fact, it is precisely for this reason that terms like genotype and phenotype are used to specify whether we are concerned with an organism's genes or its external appearance. Students of biology are most familiar with one of the causes of uncertainty in the relationship between genes and characters, namely, the relative dominance of different alleles of a given gene. With dominance, a particular phenotype can be produced by several different genotypes. The uncertainty works in the other direction as well: A single genotype can produce many different phenotypes, depending on various contingencies encountered during development. That is, the phenotype is the outcome of a complex series of developmental processes that are influenced by environmental factors as well as by genes. Different environments can have an effect on the outcome of development that is as profound as that produced by different genes. This phenomenon, which is nearly universal, is called phenotypic plasticity.