Context: The following passage describes the effects of a gene mutation, which is a permanent change in a gene. Read the passage and then follow the instructions below.

The eyes of fruit flies look red because they contain molecules called pigments, which color the eyes red. Cells in the eyes of fruit flies have parts that make these pigments from other molecules.
The molecules that will become pigments are brought inside these cell parts by a protein called a transporter. This transporter protein is encoded by the w gene.
Scientists in a lab found a fruit fly that had white eyes. This fly had a mutation in its w gene. Compared to the w gene without a mutation, the mutated w gene encoded a form of the transporter protein with a different structure.
This different form of the transporter protein could not bring molecules into the parts of the fly's eye cells where pigments are made. So, the fly's eyes had no pigments.
Figure: a white fly eye (left) and a red fly eye.
Complete the sentence.
The mutation in the () affected the structure and function of the ().
A. transporter protein . . . w gene
B. w gene . . . transporter protein
Determine the correct option from the provided choices and reply with its corresponding letter.

B