Combinatorial control of eve gene expression in fruit fly development. (a) A Drosophila embryo stained with fluorescent antibodies that recognize the protein even-skipped (product of eve), showing its striped pattern of expression. (b) The graphs represent the relative levels and positions along the length of the embryo of even-skipped (top) and four transcription factors that regulate its expression (bottom). Specific combinations of transcription factors activate the eve gene.