Final answer:
Homeotic loci, primarily comprised of Hox genes, are responsible for specifying the adult structures and functions of developing cells. These genes encode transcription factors that determine an organism's body plan, including segmentation and limb placement, illustrating a conserved evolutionary strategy for development.
Step-by-step explanation:
During development, homeotic loci specify the adult structures and functions of developing cells. These loci are primarily represented by Hox genes, which play a critical role in defining the body plan of an organism. For example, a Hox gene mutation in the fruit fly can lead to the formation of legs where antennae should be because these structures are controlled by Hox gene activity in their respective body segments during development. The homeotic genes that contain sequences known as homeoboxes encode transcription factors that are pivotal in determining the general body plan of an animal, such as the number of body segments, placement of appendages, and the anterior-posterior orientation.
The importance of Hox genes extends beyond simply embryonic development, as they also initiate and terminate the expression of specialized cells and tissues during organogenesis. This process is evident in both fruit flies and nematodes, where segmentation and cell lineage have been extensively studied. Hox genes have been observed in all animals, indicating a conserved evolutionary strategy for development.