Lecture 36

Abstract

It is the task of developmental genetics to elucidate the role of the genetic information in the complex of developmental processes leading from egg to adult. We have already seen an association of visible traits, as well as developmental tendencies, with hereditary factors, as shown in genetic crosses. But even though we have been able to follow genetically controlled changes in the expression of a character back to earlier stages in development, we are in most cases still fairly far from the primary actions of genes. Models providing deeper insight into the mode of action of individual genes and the interplay of various genes have been useful up till now only on the chemical level. One area close both to chemical and histological levels is the genetic control of eye pigments, which are laid down in granules. Precursors of the pigments in the Lepidoptera and Diptera arise not only in the cells which form the pigment, but also earlier in various tissues from which they are released into the blood. So it is possible to supply a missing precursor to the eye cells of a mutant which cannot form a particular pigment, and this is done by a normal implant. Certain intracellular defects of the mutant cells can also be corrected by contributions of other cells.