CANALIZATION - A MOLECULAR-GENETIC PERSPECTIVE

The phenomenon of 'canalization' - the genetic capacity to buffer deve lopmental pathways against mutational or environmental perturbations - was first characterized in the late 1930s and early 1940s. Despite en ormous subsequent progress in understanding the nature of the genetic material and the molecular basis of gene expression, there have been f ew attempts to interpret the classical work on canalization in molecul ar genetic terms. Some recent findings, however, bear on one form of c analization, 'genetic canalization', the stabilization of development against mutational effects. These data indicate that co-expressed para logous genes can function as mutual 'back-up' elements in developmenta l processes. Paralogues, however, are far from the only basis of canal ization: other genetic sources can be readily envisaged and some of th ese are described here. The evolutionary questions about genetic canal ization and the mechanistic questions about developmental instability that still need to be addressed are also briefly discussed.