ical " ▁home od om ain ▁consisting ▁of ▁ 6 3 ▁am ino ▁ac ids . ▁According ▁to ▁their ▁conser ved ▁intr on – ex on ▁structure ▁and ▁to ▁unique ▁cod om ain ▁architect ures ▁they ▁have ▁been ▁grouped ▁into ▁ 1 4 ▁distinct ▁classes : ▁HD - Z IP ▁I ▁to ▁IV , ▁B EL , ▁K NO X , ▁PL IN C , ▁W O X , ▁P HD , ▁D DT , ▁N D X , ▁L D , ▁SA WA DE E ▁and ▁P IN TO X . ▁Conserv ation ▁of ▁cod om ains ▁suggests ▁a ▁common ▁e uk ary otic ▁ancest ry ▁for ▁T A LE ▁and ▁non - TA LE ▁home od om ain ▁prote ins . ▁ ▁Human ▁home obox ▁gen es ▁ ▁The ▁H ox ▁gen es ▁in ▁humans ▁are ▁organized ▁in ▁four ▁chrom os om al ▁clusters : ▁ ▁Para H ox ▁gen es ▁are ▁analog ously ▁found ▁in ▁four ▁areas . ▁They ▁include ▁CD X 1 , ▁CD X 2 , ▁CD X 4 ; ▁G S X 1 , ▁G S X 2 ; ▁and ▁P D X 1 . ▁Other ▁gen es ▁considered ▁H ox - like ▁include ▁E V X 1 , ▁E V X 2 ; ▁GB X 1 , ▁GB X 2 ; ▁ME O X 1 , ▁ME O X 2 ; ▁and ▁M N X 1 . ▁The ▁NK - like ▁( N K L ) ▁gen es , ▁some ▁of ▁which ▁are ▁considered ▁" Meta