Homeotic Genes Determine Specialization of Segments

Edward B.Lewis at the California Institute of Technology in Pasadena was interested in questions concerning certain developmental changes in the Drosophila fly and how the genes causing them cooperate during body segmentation. The answers he got, laid the foundation of one of the most surprising discoveries in developmental biology - the same type of genes which controls the early embryonic development of Drosophila also controls the early embryogenesis of a lot of higher organisms, including man. This means that the genetic control mechanisms have been preserved roughly unchanged through 650 million years of evolution!

A starting point for Lewis in his research on the genetic basis for so-called homeotic transformations during early embryonic development was his work with the now famous Drosophila-mutant with four wings instead of two. Homeotic genes control specialization of the segments. In the mutant-case inactivity of the first gene in a complex of homeotic genes (the bithorax complex) caused other homeotic genes to duplicate the segment with two wings. Lewis' pioneering work on the bithorax genes led to his discovery of the co-linearity principle. According to this principle there is a co-linearity in time and space between the order of the genes in the bithorax complex and their effect regions in the segments. This discovery has had a very large influence on later developmental research.