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Evolution of the Hox Gene Cluster

  1. David EK Ferrier

Published Online: 15 AUG 2012

DOI: 10.1002/9780470015902.a0023989



How to Cite

Ferrier, D. E. 2012. Evolution of the Hox Gene Cluster. eLS. .

Author Information

  1. University of St Andrews, East Sands, St Andrews, The Scottish Oceans Institute, Fife, UK

Publication History

  1. Published Online: 15 AUG 2012


The Hox genes are a family of developmental control genes containing a homeobox motif, and tend to be organised in distinctive clustered arrays in animals. Organisation within the cluster can relate to how the genes function. Whilst much has been discovered about the Hox gene cluster in traditional model systems of developmental biology, increasing amounts of data from a wider variety of species are illuminating more about the nature of the Hox cluster deep in animal ancestry, as well as revealing the evolutionary flexibility and derivations along present-day lineages. The consensus view of the Hox cluster is that it patterns the anterior–posterior axis of bilaterally symmetrical (bilaterian) animals and exhibits the phenomenon of colinearity. There is, however, much evolutionary change within this system. This diversity in the Hox system is linked to the evolution of animal diversity and informs our understanding of the pre-bilaterian origins of the Hox genes themselves.

Key Concepts:

  • Spatial colinearity is the phenomenon whereby the order of the expression domains of the Hox genes along the anterior–posterior axis of the embryo corresponds with the order of the genes along the chromosome.

  • Temporal colinearity is a further form of colinearity in which the Hox genes in some taxa are activated progressively, with the earliest time at which a gene is activated matching its position within the Hox cluster.

  • Anterior–posterior patterning by the Hox genes is distinct from the initial determination of the anterior–posterior axis and instead involves the specification of different developmental fates within the anterior–posterior axis of an embryo. This is one of the major roles of the Hox genes within the bilaterians, but the Hox genes do have further roles in development subsequent to this anterior–posterior patterning function.

  • A range of Hox gene organisation has evolved across different lineages, forming organised, disorganised, split and atomised Hox clusters, such that the Hox genes of some species are not actually organised into a Hox gene cluster.


  • homeobox;
  • bilaterian;
  • cnidarian;
  • Hox gene;
  • Hox cluster