The Antennapedia (Antp) gene is a key homeotic (Hox) gene in Drosophila melanogaster that controls segment identity along the anterior-posterior axis during development. Specifically, Antp expression defines the identity of the second thoracic segment (T2), which gives rise to legs.

Expression of Antennapedia

Antp is expressed in thoracic segments, mainly the second thoracic segment, and is critical for proper development and differentiation of leg structures. Its expression is spatially regulated to avoid the head region, ensuring proper segmental patterning.

Molecular Function

One of the functions of Antp is to repress genes responsible for antennal development within the thoracic segments. Loss of Antp function allows antenna-specific genes to be expressed ectopically in these segments, while gain-of-function mutations or ectopic expression in the head induce leg development in place of antennae.

Effects of Antp Mutation

A mutation causing ectopic expression of Antp in the head (where antennae normally develop) results in the antenna transforming into leg-like structures—a classic homeotic transformation. Conversely, a recessive loss-of-function mutation (Antp-) in thoracic segments can cause leg to antenna transformations.

Analysis of Statements

• Statement A: Antp gene ectopically expresses in the head region in Antp mutation causing antenna-to-leg transformation — true.

• Statement B: Antp represses genes that induce antennal development — true.

• Statement C: Antp forming a concentration gradient to affect head development is inaccurate; Antp is expressed in thorax, and its function is more binary than gradient based — false.

• Statement D: Homozygous recessive Antp mutation transforming leg to antenna is true.

Correct Combination

The combination (4) A, B, and D accurately describes Antennapedia gene function.