How do homeotic genes regulate development in drosophila?

Hint: Homeotic genes are the genes which control the pattern of body formation, during early embryonic development. . A homeotic protein can activate one gene but it represses another, and produces effects which are complementary and necessary for the development of an organism.

Complete answer:
Homeotic genes contain a sequence of DNA referred to as a homeobox, that encodes a segment of sixty amino acids within the homeotic transcription factor protein. Homeotic genes function by activating or inhibiting other genes called realisator genes. These realisator genes are responsible for the development of the final structures such as eyes and wings. Homeotic genes thus ensure that the final structures are present at the right place.
Homeotic genes of the Antennapedia and bithorax complexes control Drosophila development by encoding DNA-binding proteins. These regulate the transcription of targeted genes. As, either the presence or absence of the DNA-binding proteins hinders development, it is crucial to regulate the spatial patterns of expression for normal development. Several gene products are required to properly regulate the expression of Antennapedia and bithorax complex genes, but few (if any) are dedicated only for the regulation of these genes. One of the pleiotropic activators of homeotic genes in Drosophila is the Brahma gene. This gene encodes a protein similar to a yeast protein which is required for transcriptional activation of multiple tightly regulated genes. Other components of this system may be protected as well, suggesting that the biochemical basis for induced gene expression in single-celled organisms may have more in common with programmed developmental pathways in multicellular organisms than previously thought.

Note: Homeotic genes contain a sequence of DNA known as a homeobox, this gene encodes a segment of sixty amino acids within which the homeotic transcription factor protein. If a mutation occurs in the homeobox of any of the homeotic genes, then an organ of that organism will not develop correctly. For example, in Drosophila (fruit flies), mutation of a particular homeotic gene results in altered transcription, leading to the growth of legs on the head instead of an antenna; this is known as the antennapedia mutation.