Practice question

Bithorax complex comprises three protein-coding homeotic genes Ultrabithorax, abdominal-A, and Abdominal-B arranged colinearly along chromosome 3R with cis-regulatory domains bxd, iab-2 to iab-9 controlling parasegment-specific expression from fifth to fourteenth parasegment, corresponding to third thoracic through eighth abdominal segments. Regulatory domains drive tissue-specific patterns activating UBX in T3, abd-A in A1-A4, Abd-B in A5-A8. Deletion transforms posterior segments toward second thoracic identity. Head and anterior thorax specification relies on Antennapedia complex, while antenna formation depends on homothorax and Distal-less, distinct from BX-C control, illustrating functional subdivision of homeotic clusters along anteroposterior axis for segment identity determination.