Practice question

Anterior structures in Drosophila are patterned by Bicoid, a homeodomain transcription factor functioning as classic morphogen. Its mRNA is localized to anterior pole of the oocyte through cytoskeletal anchoring, and after fertilization translation produces protein that diffuses posteriorly forming exponential gradient in syncytial embryo. Nuclei exposed to high Bicoid activate anterior gap genes including hunchback, orthodenticle and empty spiracles promoting head and thoracic identity. Lack of Bicoid deletes anterior segments and transforms them into posterior telson via ectopic Caudal, while ectopic anterior transplantation duplicates head structures posteriorly, confirming morphogen role.