From genes to individuals: developmental genes and the generation of the phenotype.

The success of the genetic approach to developmental biology has provided us with a suite of genes that are involved in the regulation of ontogenetic pathways. It is therefore time to ask whether and how such genes might be involved in the generation of adaptive phenotypes. Unfortunately, the current results do not provide a clear answer. Most of the genes that have been studied by developmental biologists affect early embryonic traits with significant effects on the whole organism. These genes are often highly conserved which allows us to do comparative studies even across phyla. However, whether the same genes are also involved in short-term ecological adaptations remains unclear. The suggestion that early acting ontogenetic genes may also affect late phenotypes comes from the genetic analysis of quantitative traits like bristle numbers in Drosophila. A rough mapping of the major loci affecting these traits shows that these loci might correspond to well known early acting genes. On the other hand, there are also many minor effect loci that are as yet uncharacterized. We suggest that these minor loci might correspond to a different class of genes. In comparative studies of randomly drawn cDNAs from Drosophila we find that there is a large group of genes that evolve fast and that are significantly under-represented in normal genetic screens. We speculate that these genes might provide a large, as yet poorly understood, reservoir of genes that might be involved in the evolution of quantitative traits and short-term adaptations.