Functional genomics strategies can complement traditional genetic approaches to identifying genes underlying complex behavioral traits. In an Advanced Online Publication in Nature Genetics Toma et al. describe an illustrative example of a study aimed at defining genes involved in geotaxis in Drosophila melanogaster (Nature Genetics, 3 June 2002, DOI:10.1038/ng893).
They examined differential gene expression levels, using microarray technology, in samples from fly strains with extreme geotaxis capacities. About 5% of genes showed differential expression. Toma et al. tested four candidate genes by examining single-gene mutant strains and found that three had a clear effect on geotaxis. The authors emphasize that "microarray analysis can be used as a starting point for narrowing down candidate genes involved in complex genetic processes … and offers a promising approach to previously intractable molecular analysis of behavior."