Body Plan

A body plan is the blueprint for the way the body of an organism is laid out. Each species of multicellular organism—plant, fungus, red algae, slime mold, among others—has a body plan. This article is about animal body plans.

An animal's symmetry, its number of body segments and limbs are all aspects of its body plan. One of the key issues of developmental biology is the evolution of body plans as different as those of a starfish, or a mammal, which come from a close common biological heritage-both are deuterostomes. One issue in particular is how radical changes in body plans have occurred over geological time. The body plan is a key feature of an organism's morphology and, since the discovery of DNA, developmental biologists have been able to learn a lot about how genes control the development of structural features through a cascade of processes in which key genes produce morphogens, chemicals that diffuse through the body to produce a gradient that acts as a position indicator for cells, turning on other genes, some of which in turn produce other morphogens. A key discovery was the existence of groups of homeobox genes, which are responsible for laying down the basic body plan in animals. The homeobox genes are remarkably conserved between species as diverse as the fruit fly and man, the basic segmented pattern of the worm or fruit fly being the origin of the segmented spine in man. The field of animal evolutionary developmental biology, which studies the genetics of morphology in detail, is now a rapidly expanding one, with many of the developmental genetic cascades, particularly in the fruit fly drosophila, now catalogued in considerable detail.

Body plan is the basis for distinguishing animal phyla, and there are 35 different basic animal body plans, each corresponding to distinct animal phyla.