Plans A & B correspond to alternative genotypes. Under any of a wide variety of Environments (1, 2, & 3), these genotypes will determine the course of a zygote in development to produce alternative phenotypes, corresponding to Organisms A & B. For example, persons conceived with a Trisomy-21 karyotype [Plan B] will have Down Syndrome, regardless of pre- or post-natal environment.

Environments A & B include suites of factors that predispose organisms one way or another. Depending on which particular factors are present, the genetic program make take any zygote and produce alternative phenotypes, corresponding to Organisms A & B. For example, although genetic makeup predisposes humans to be able to use language, persons born in Iceland [Environment A] are likely to grow up speaking Icelandic, regardless of their ethnic background.

Alternative Genotypes A & B interact with Environments I & II to produce a range of organismal phenotypes, which are not necessarily predictable. If the phenotypic value of Organism AI > BI > AII > BII, note that Environment I always produce a superior type to Environment IIl, and Genotype A always produces a better phenotype than B in any one environment. However, Genotype B in Environment I is superior to A in II. Prediction of the phenotype requires a knowledge of both genetics and environment.

Figures ©2002 by Griffiths et al.; all text material ©2006 by Steven M. Carr