Homeobox genes are a diverse set of genes controlling the embryonic development of animals. These genes are characterized by having a 180-nucleotide DNA sequence, the homeobox, which encodes a 60-amino acid protein domain, the homeodomain, of the homeodomain protein. Most of the homeodomain proteins function as transcription factors and participate in the developmental biology of the animal. The homeobox genes have earlier been classified into superclasses, classes, subclasses or groups.
In a study published in the 26 October, 2007, issue of BMC Biology, Holland et al., proposed a revised classification and nomenclature of human homeobox genes. The classification scheme is based on gene class and gene family. Each gene class contains one or more gene families, and each gene family contains or or more genes.
The study recognized 102 homeobox gene families in the human genome. And eleven homeobox gene classes were identified: ANTP, PRD, LIM, POU, HNF, SINE, TALE, CUT, PROS, ZF and CERS. Out of these 11 classes, the ANTP and PRD classes are the largest. A total of 300 homeobox loci were identified, out of which 235 are probable functional genes and 65 are probable pseudogenes.
The study also sheds light on the evolution of human homeobox genes. Read the full paper here.