Homeotic Genes
The human body is composed of several trillion cells, all coming from the same single fertilized egg, having the same genes, yet almost all of them have become specialized to perform certain tasks. This is because not all genes in a cell are activated at the same time.
Several of the proteins that can bind to DNA come from genes which, when expressed, give the cell a specialty according to its position in the body.
The term homeotic genes applies to these genes that encode proteins that bind to specific DNA sequences, and thus influence the organism’s subsequent development.
These specific sequences of DNA are called homeoboxes. See above. The proteins that arise from a gene containing a homeobox sequence can bind to another gene in turn.
This triggers a cascade of gene expressions resulting in the segmentation of the embryo.
We thus can see how certain “master” homeotic genes control the transcription of a set of secondary genes that in turn influence the activity of other target genes at a lower level in the hierarchy. These genes will then produce the proteins used to build the structures and organs of the body.
