Occurrence and arrangement of Hox complexes in metazoans

Hox genes have not been detected in choanoflagellates, single-celled organisms that represent the sister clade to metazoans, but they are present in all metazoans. In the vertebrate lineage (exemplified by the mouse), the entire complex has been duplicated twice, resulting in four Hox complexes. Such events have produced duplicated genes that were later co-opted to new developmental functionsHox genes have not been detected in choanoflagellates, single-celled organisms that represent the sister clade to metazoans, but they are present in all metazoans. In the vertebrate lineage (exemplified by the mouse), the entire complex has been duplicated twice, resulting in four Hox complexes. Such events have produced duplicated genes that were later co-opted to new developmental functions

Bilaterians Choanoflagellates (none detected) Sponges I I I I Cnidarians - - lab pb bcd £92”; Dtd Scr ltz Amp be abd—A Adb-B vFruithy I I I I I I I I%\-I—I—I— ~ Onychophoran J—I—I—I—H—I—I—I— ‘\ Nematode CI—I—\\—I—I—\\—I—I— - 77777777777777 Priapulid I I I I I I - - - - Polychaete —I—I—I—I—I—I—I—I—I—I— LeechesI IIIIII Nemertean J—I—I—I—I—I— Flatworms H—I—I—I—I—H— Gastropod I I I I I I Brachiopod I I I I I I I I I 1 2 3 4 5 6 7 8 9 10 11 12 13 I I I I I I I I I I I-