Required for segmental identity of the second through eighth abdominal segments. Once a pattern of abdA expression is turned on in a given parasegment, it remains on the more posterior parasegment, so that the complex pattern of expression is built up in the successive parasegments. The abdA product appears to repress expression of Ubx whenever they appear in the same cell, but abdA is repressed by AbdB only in the eight and ninth abdominal segments. Belongs to the Antp homeobox family.