Genetic control of size in Drosophila

During the past ten years, significant progress has been made in understand ing the basic mechanisms of the development of multicellular organisms. Gen etic analysis of the development of Caenorhabditis elegans and Drosophila h as unearthed a fruitful number of genes involved in establishing the basic body plan, patterning of limbs, specification of cell fate and regulation o f programmed cell death. The genes involved in thee developmental processes have been conserved throughout evolution and homologus genes are involved in the patterning of insect and human limbs. Despite these important discov eries, we have learned astonishingly little about one of the most obvious d istinctions between animals; their difference in body size. The mass of the smallest mammal, the bumble-bee bat, is 2 g while that of the largest mamm al, the blue whale, is 150 t or 150 million grams. Remarkable, even though they are in the same class, body size can var up to 75-million-fold. Furthe rmore, this body growth can be finite in the case of most vertebrates or it can occur continuously throughout life, as for trees, molluscs and large c rustaceans. Currently, we know comparatively little about the genetic contr ol of body size. In this article we will review recent evidence from verteb rates and particularly from Drosophila that implicates insulin/insluin-like growth factor-I and other growth pathways in the control of cell, organ an d body size.