Segmentation

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 arthropods, vertebrates and annelid worms.

A millipede: a really obvious example of segmentation

Vertebrates have a segmented vertebral column.

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 genes whose proteins bind to the regulatory regions of target genes. The latter then activate or repress cell processes which direct the final development of the organism.^[1][2]

Furthermore, the sequence of these control genes show co-linearity: the order of the 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.^[3][4]

Each of the genes contains a homeobox, a remarkably conserved DNA sequence. This suggests the complex itself arose by gene duplication.^[5][6][7]

In his Nobel lecture, Lewis said "Ultimately, comparisons of the [control complexes] throughout the animal kingdom should provide a picture of how the organisms, as well as the [control genes] have evolved".^[8]