Final answer:
The HOM genes, which are part of the Hox gene cluster, control the development of specific limbs on body segments in Drosophila melanogaster. Mutations in these master control genes can result in dramatic changes, such as legs growing in place of antennae.
Step-by-step explanation:
In Drosophila melanogaster, the "decision" about which type of limb will develop on a given body segment is controlled by the HOM (homeotic) genes. The HOM genes are a subset of the Hox gene cluster, which is responsible for defining the body plan and the type of appendages that develop in specific body segments. A well-studied example of a Hox gene is the Antennapedia gene in fruit flies. An Antennapedia mutant illustrates the crucial role these genes play in appendage development, as seen with legs growing in the place of antennae where they normally wouldn't. Hox genes are a set of highly conserved master control genes that regulate the expression of many other genes during embryonic development to ensure the proper formation of body segments and their respective limbs. It's important to note that a single mutation in one of these Hox genes can lead to dramatic changes in the body plan, such as an extra pair of wings or legs where antennae should grow.