The basic body structure of the fly in the figure above is determined by a cluster of:

a. repressor genes.
b. hox genes.
c. polypeptides.
d. frameshift mutations.

Ans. B. Hox genes.

Hox genes (homeobox genes) can be defined as a group of related genes, which specify regions of an body plan of an organism's embryo along its head-tail axis. Given figure represents body plan in fruit fly, in which has eight Hox genes, clustered into two complexes.

These genes include labial (for head involution),  proboscipedia (for labial abd maxillary pulps), deformed (maxillary and mandibular segments), sex combs reduced (for cephalic and thoracic development), antennapedia (pair of legs and wings), ultrabithorax (pair of legs halteres), abdominal-A and abdominal-B (for abdomen).

Thus, the correct answer is option (B).