▁of ▁gen es ▁st ems ▁from ▁their ▁unique ▁behavior ▁and ▁arrangement ▁in ▁the ▁gen ome . ▁H ox ▁gen es ▁are ▁typically ▁found ▁in ▁an ▁organized ▁cluster . ▁The ▁linear ▁order ▁of ▁H ox ▁gen es ▁within ▁a ▁cluster ▁is ▁directly ▁correl ated ▁to ▁the ▁order ▁they ▁are ▁expressed ▁in ▁both ▁time ▁and ▁space ▁during ▁development . ▁This ▁phenomen on ▁is ▁called ▁col ine ar ity . ▁▁ ▁Mut ations ▁in ▁these ▁home otic ▁gen es ▁cause ▁disp lacement ▁of ▁body ▁segments ▁during ▁emb ry onic ▁development . ▁This ▁is ▁called ▁e ct op ia . ▁For ▁example , ▁when ▁one ▁gene ▁is ▁lost ▁the ▁segment ▁develop s ▁into ▁a ▁more ▁anterior ▁one , ▁while ▁a ▁mut ation ▁that ▁leads ▁to ▁a ▁gain ▁of ▁function ▁causes ▁a ▁segment ▁to ▁develop ▁into ▁a ▁more ▁posterior ▁one . ▁Fam ous ▁examples ▁are ▁An ten nap edia ▁and ▁b ith or ax ▁in ▁D ros oph ila , ▁which ▁can ▁cause ▁the ▁development ▁of ▁legs ▁instead ▁of ▁anten na e ▁and ▁the ▁development ▁of ▁a ▁dup licated ▁thor ax , ▁respectively . ▁ ▁In ▁verte br ates , ▁the ▁four ▁par alog ▁clusters ▁are ▁partially ▁redundant ▁in ▁function , ▁but ▁have ▁also ▁acquired ▁several ▁derived ▁functions . ▁For ▁example , ▁H ox A ▁and ▁H ox D ▁specify ▁segment ▁identity ▁along ▁the ▁lim b ▁axis . ▁Specific ▁members ▁of ▁the ▁H ox ▁family ▁have ▁been ▁imp licated ▁in ▁v asc ular ▁rem od eling , ▁ang i ogen esis , ▁and ▁disease ▁by ▁orch estr ating