Genes controlling segment identity:
Segment number, polarity, and position established by gap, pair-rule, segment polarity hierarchy, but final morphological identity depends on homeotic selector genes clustered in Antennapedia and Bithorax complexes. These selectors encode homeodomain factors regulating batteries of realizator genes governing cuticle pigmentation, bristle pattern, limb type, and nervous connectivity. Gap genes specify regions, pair-rule provide periodicity, segment polarity maintains borders, none confer segment-specific character. Homeotic selectors act downstream interpreting segmental address and executing distinct programs, explaining why loss or ectopic expression transforms one segment toward another without altering count or polarity.
Ref: Gilbert, Developmental Biology, 12th ed., Chapter 20: Homeotic selector genes - ANT-C and BX-C conferring segment identity.