Genetics in Learning and Memory

The power of genetics has been clearly demonstrated in studies of embryonic development. Systematic searches for mutant phenotypes during embyogenesis in Drosophila (Nusslein-Volhard and Wieschaus, 1980; Johnston and NussleinVolhard, 1992; Wieschaus, 1996) and zebrafish (Grunwald and Eisen, 2002) have uncovered most of the genes controlling embryonic pattern formation. The number of genes involved is limited, and they can be categorized into specific functional groups according to their phenotypic effects. Many of the corresponding genes have been characterized molecularly, thereby identifying components of gene regulation and cell signaling pathways. Genes first discovered in flies have subsequently been identified in vertebrates, and basic genetic mechanisms controlling early development of invertebrates have been shown to be conserved in vertebrate systems. Thus, a driving force behind analysis of development has been gene discovery in flies, which in turn has provided experimental and conceptual tools to dissect mechanisms of morphogenesis in both invertebrate and vertebrate species.