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.

As in humans, hunger in mice depends on how much food a mouse has eaten. When a mouse eats, its hunger is controlled by the leptin receptor protein.
The leptin receptor protein receives signals from the mouse's body when the mouse eats. The leptin receptor protein then sends signals to the brain, telling it that the mouse is full. The leptin receptor protein is encoded by the OB-R gene.
A certain mouse had a mutation in the OB-R gene. Compared to the OB-R gene without a mutation, the mutated OB-R gene encoded a form of the leptin receptor protein with a different structure.
This different form of the leptin receptor protein was unable to send signals to the mouse's brain. This mouse continued to eat as if it did not feel full. As a result, the mouse ate a large amount of food and became obese.
Figure: an obese mouse (left) and a mouse of average weight.
Complete the sentence.
The mutation in the () affected the structure and function of the ().
A. leptin receptor protein . . . OB-R gene
B. OB-R gene . . . leptin receptor protein
Answer with the option's letter from the given choices directly.

B