Gene function

The problem of gene function - of the relationships between hereditary mate rial and the characteristics of organisms - preceded the rediscovery of Men del's laws and accompanied the development of genetics in the XXth century. Molecular biologists replaced the simple gene-character relationship by tw o relationships: the first, between genes and proteins, was well defined, w hereas the second between proteins and the complex structural and functiona l characteristics of organ isms remained unknown. I will describe in this a rticle the experimental approaches which helped to characterize during the last twenty years the relationships between proteins and characters. Four p rinciples of macromolecular organization emerged from these studies: conser vation of the elementary components during evolution, existence of pathways and networks, pleiotropy and redundancy. These principles are the explanat ion of the surprising experimental observations that have been made in rece nt years. The existence of these principles makes problematic any predictio n on the consequences of gene modification. It both sounds the death-knell of the simplistic reductionist approach of many biologists, whereby genes w ere considered as responsible for specific functions, and definitely preven ts the distribution of genes in separate, well defined categories. (C) 2000 Academie des sciences/Editions scientifiques et medicales Elsevier SAS.