Genes and Developmental Pathways

The way in which genes control the growth and development of an organism is a central problem in biology, and one which is currently under study in diverse forms from phage to man. I would like to discuss an approach to this problem which makes use of a series of pseudoallelic genes in Drosophila. Such series of closely linked genes with related effects have, in several instances, been profitably exploited in the bacteria to learn more about how genes control biochemical pathways. Striking examples are the linked genes controlling histidine biosynthesis in Salmonella (Demerec and Hartman, 1959; Ames and Hartman, 1962), or lactose utilization in Escherichia coli ( Jacob and Monod, 1961a,b). It may be anticipated that pseudoallelic series affecting morphological traits, such as the case to be described below, can also be profitably exploited to learn more about how genes control developmental pathways.