What is Segmentation?
[[File:Harpaphe haydeniana 002.jpg|thumb|230px|right|A [[millipede]]: a really obvious example of segmentation]] [[Image:Gray 111 - Vertebral column.png|thumb|125px|right|[[Vertebrate]]s have a segmented [[vertebral column]].]] '''Segmentation''' in biology means the division of some [[animal]] and [[plant]] bodies into a series of repeat sections or parts. It is common in some of the most successful groups of animals, such as [[arthropod]]s, [[vertebrate]]s and [[annelid]] [[worm]]s. Segmentation of the body allows different regions of the body to develop for different uses. == Genes regulating development == We now know a good deal about how the development of segmented animals is controlled. In a series of experiments with the fruit-fly ''[[Drosophila]]'', [[E.B. Lewis]] was able to identify a complex of [[gene]]s whose [[protein]]s bind to the regulatory regions of target genes. The latter then activate or repress [[cell]] processes which direct the final development of the organism.<ref>Lewis E.B. 1995. The ''bithorax'' complex: the first fifty years. [[Nobel Prize]] lecture. Repr. in Ringertz N. (ed) 1997. ''Nobel lectures, Physiology or Medicine''. World Scientific, Singapore.</ref><ref>Lawrence P. 1992. ''The making of a fly''. Blackwell, Oxford.</ref> Furthermore, the sequence of these control genes show ''co-linearity'': the order of the [[Locus (genetics)|loci]] in the [[chromosome]] parallels the order in which the loci are expressed along the anterior-posterior axis of the body. Not only that, but this cluster of master control genes programs the development of all higher organisms.<ref>Duncan I. 1987. The bithorax complex. ''Ann. Rev. Genetics'' '''21''', 285–319.</ref><ref>Lewis E.B. 1992. Clusters of master control genes regulate the development of higher organisms. ''J. Am. Medical Assoc''. '''267''', 1524–1531.</ref> Each of the genes contains a [[homeobox]], a remarkably [[Conserved sequence |conserved]] [[DNA sequence]]. This suggests the complex itself arose by [[gene duplication]].<r