Final answer:
Ectopic expression of the Ey gene in an area normally developing into a leg results in the development of a leg in the wrong place, like the Antennapedia mutant where a leg grows out of the fly's head instead of an antenna.
Step-by-step explanation:
If the Eyeless (Ey) gene is ectopically expressed in larval cells of the area that gives rise to a leg in Drosophila, an anomaly occurs similar to what happens in the Antennapedia mutant. Instead of growing an antenna, the fruit fly grows a leg out of its head. This is because Hox genes like Ey are master control genes that can turn on or off large numbers of other genes during embryogenesis, determining the body pattern of an organism.
Ey is analogous to the Antennapedia gene, which when mutated can lead to the transformation of antennae into legs. Hox genes specify the identity of body parts. When these genes are expressed in places where they are normally inactive, they can cause body parts to develop in incorrect locations. In this ectopic expression scenario, the leg develops instead of the appropriate structure for that location.
The effects of such ectopic gene expression are profound, showcasing how patterns of gene expression are critical for the proper development of body segments and structures. This example also illustrates how the alteration of a single Hox gene can lead to significant changes in an organism's body plan.