A homeobox is a segment of DNA about 180 base pairs long that is found within genes. It bonds with proteins in which it resides in a DNA-binding homeodomain about 60 amino acids long encoded by the homeobox. The protein is a major building block of an organisms genome structures such as appendages or antenna. Homeobox genes, or genes containing a homeobox, are thus a viable model to interpret or predict, and in manipulation control embryogenesis of these structures and thus ultimate phenotype expression of homologous structures that constitute multicellular organisms.
In 1983 Walter Jakob Gehring and his colleagues at the University of Basel, Switzerland observed the homeotic genes in the common fruit fly, or Drosophila melanogaster. Before this unique discovery, it was not thought that the same genetic mechanism, namely homeobox genes, were at play for both invertebrates and vertebrates alike.
Matthew Scott and Amy Weiner were then working with Thomas Kaufman at Indiana University in Bloomington and can also be credited to an extent. Scott said quite succinctly that,
|“||Instead of having to study genes and proteins and molecular events that are very specific to one tissue, or one developmental stage, or one organism, you can take advantage of the special attributes of whatever your experimental system is, and whatever you learn is likely to be very useful in understanding a great many other events in other tissues, stages, and creatures.||”|
Hox genes are a subgroup or subset of homeobox genes. Within vertebrates they can be found in gene clusters on chromosomes. They regulate development of the anterior to posterior axis. It is important to note that only genes in the hox cluster should be considered hox genes and the gene name hox is restricted to only hox cluster genes in vertebrates, while the homeobox is the overarching encoder for the homeotic genes to begin with.
A hox cluster is a grouping of homeotic genes, called hox genes in vertebrates. Clusters of genes turn on in sequence to determine the overall body pattern from the front to the back, and top to bottom. Genes cascade down like waves rushing ashore which then lay out increasingly localized structures. These structures which ultimately become segments of an organisms body are identified by the homeotic gene.
Hox Genes and Punctuated Equilibrium
- Main Article: Punctuated Equilibrium
Evolutionists claim that even minor mutations of hox genes could lead to an outcome of radical genome change, enabling the evolution leap of change able to produce the diversity of life observed. The outcome of evolving genomic structure is seen by evolutionists as genes potentially responsible for a punctuated equilibrium pattern of change. Hox genes and natural selection form a relationship and produce from the simplest molecule the diversity of life.
The potential of an evolutionary path in accordance with Stephen Jay Gould's punctuated equilibrium through hox gene manipulation ultimately requires extrapolation from what is observed by manipulating hox genes, namely different phenotype disfigurements or expression fates. The expression fate of hox gene clusters when experimented on by scientists is always of a phenotype change, and conclusively very limited for true Gouldian punctuated equilibrium.
Scientists have recently developed specific organism models to conduct future testing of this very exciting field of genetic research. Allowing the organism Parhyale hawaiensis to be studied genetically has opened up new doors into the workings of evolutionary development within segments that make up the organisms full body.
- The Homeobox Page by Thomas R. Bürglin for Department of Biosciences and Nutrition
- The Fruitful Fruit Fly: Discovering the Homeobox by Howard Hughes Medical Institute
- The Evolutionary Secret of Body Segmentation by David Pescovitz
- Probing the evolution of appendage specialization by Hox gene misexpression in an emerging model crustacean Anastasios Pavlopoulos, Zacharias Kontarakis, Danielle M. Liubicich, Julia M. Serano, Michael Akam, Nipam H. Patel, and Michalis Averof. Proc Natl Acad Sci U S A. 2009 August 18; 106(33): 13897–13902.
- A muscle-specific transgenic reporter line of the sea anemone, Nematostella vectensis Proc. Natl. Acad. Sci. USA 2010 107 (1) 104-108
- Establishment of Spatial Patterns of Gene Expression During Early Vertebrate Development: Hox Genes by Dr. Derrick Rancourt for Department of Medical Biochemistry, University of Calgary
- Control of Segmental Identity in Drosophila: Homeotic Genes by Dr. William Brook for Department of Medical Biochemistry, University of Calgary