Appears to control physiological cell functions rather than pattern formation during embryogenesis. First detected in the posterior region of the blastoderm embryo. In later stages of embryonic development, detected in the posterior portion of the midgut, in the developing malpighian tubules, in a subset of ventral somatic muscles, in the developing CNS and in Bolwig's organ. Belongs to the paired homeobox family. Bicoid subfamily.