Walking on the chromosome: Drosophila and the molecularization of development
While the fruit fly Drosophila melanogaster played a crucial role in the establishment of genetics as a science, the molecularization of genetics in the 1950s and 1960s was largely a result of work involving microorganisms, especially the colon bacillus Escherichia coli and its bacteriophages (see Chapter 2 by Holmes, this volume). However, beginning in the 1970s, Drosophila came back on the scene as one of the major laboratory organisms of molecular biology, especially for research on the molecular basis of development. For example, in 1984, molecular work on Drosophila led to the discovery of the homeobox, an evolutionarily highly conserved DNA sequence element with a length of 180 base pairs that is found in eukaryotic organisms from yeast to humans. The homeobox codes for a DNAbinding domain, that is, a part of a protein molecule that makes this molecule bind to DNA in a specific manner. Genes containing a homeobox often have a gene regulatory function. In insects, such genes seem to be involved in important developmental decisions, for example, the decision as to which body segments different parts of the embryo should develop into. Some homeobox genes perform a similar function in vertebrates. Even though the various roles of different homeobox genes are only beginning to be understood, there can be no doubt that the discovery of the homeobox was a crucial event in the molecularization of developmental biology (Gehring 1985, 1998).