A fascinating feature of pattern genetics is that the dramatic phenotypic changes are primarily due to small changes in the gene that determines the sizes and positions of pattern elements. This discovery is in accord with the principal theory for the evolution of mimicry. The theory proposes that initial mimicry is achieved by a single mutation that has a large effect on the phenotype, which immediately gives the organism some protection, and is then refined by so-called modifier genes with lesser phenotypic effects. Consequently, if the genes for wing pattern and color were normal functioning genes, a single mating would produce several phenyotypically different offspring, making the ability for mimicry to evolve very difficult.