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.

Muscle movement is controlled by charged atoms called ions. Ions move in and out of muscle cells through tube-like structures called channels.
One of these channels is made from the chloride channel protein. The chloride channel protein is encoded by the CLCN1 gene.
A certain person had a mutation in the CLCN1 gene. Compared to the CLCN1 gene without a mutation, the mutated CLCN1 gene encoded a form of the chloride channel protein with a different structure.
This different form of the chloride channel protein allowed fewer ions than normal to travel through it. The person with the mutation had muscles that were slow to relax, which resulted in muscle stiffness. Having muscle stiffness due to a mutation in the CLCN1 gene is called Thomsen disease.
Figure: muscles in the human body.
Complete the sentence.
The mutation in the () affected the structure and function of the ().
A. chloride channel protein . . . CLCN1 gene
B. CLCN1 gene . . . chloride channel protein
Answer with the option's letter from the given choices directly.
Answer: B