Organization of an echinoderm Hox gene cluster

The Strongylocentrotus purpuratus genome contains a single ten-gene Hox com plex >0.5 megabase in length. This complex was isolated on overlapping bact erial artificial chromosome and P1 artificial chromosome genomic recombinan ts by using probes for individual genes and by genomic walking. Echinoderm Hox genes of Paralog Groups (PG) 1 and 2 are reported. The duster includes genes representing all paralog groups of vertebrate Hox clusters, except th at there is a single gene of the PG4-5 types and only three genes of the PG 9-12 types. The echinoderm Hox gene cluster is essentially similar to those of the bilaterally organized chordates, despite the radically altered pent ameral body plans of these animals.