A homologue of the "Dscam" protein in "Drosophila melanogaster" has 38,016 isoforms arising from four variable exon clusters (12, 48, 33 and 2 alternatives, respectively). By comparison, the entire "Drosophila melanogaster" genome only has 15,016 genes. The diversity of isoforms from alternative splicing of the Dscam1 gene in "D. melanogaster" allows every neuron in the fly to display a unique set of "Dscam" proteins on its cell surface. "Dscam" interaction stimulates neuronal self-avoidance mechanisms that are essential for normal neural circuit development.