Antennapedia

Antennapedia is a hox gene first discovered in Drosophila which controls the placement of legs. A loss-of-function mutation in the regulatory region of this gene can result in the development of the second leg pair into ectopic antennae. By contrast gain-of-function alleles convert antenna into ectopic legs.

This is just one illustration of the tendency of organisms to exhibit variations on a theme, modulated repetition. Legs and antennae are related much as molars and incisors or fingers and thumbs, arms and legs are.

Antennapedia also refers to a gene complex in Drosophila which is responsible for formation and differentiation of the thoracic and head segments of the fly's body.