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.

Keratins are strong proteins that provide structure and protection for many tissues in the human body. For example, the tissue on the inside of the mouth, called epithelium (ep-i-THEEL-i-um), is protected by a tough layer made of many types of keratin proteins connected together. One type of keratin protein is encoded by the KRT13 gene.
A certain person had a mutation in the KRT13 gene. Compared to the KRT13 gene without a mutation, the mutated KRT13 gene encoded a form of the keratin protein with a different structure.
This different form of the keratin protein could not connect to other keratin proteins.The person with the mutation had mouth epithelium that was easily damaged by simple activities like eating and brushing teeth.
Figure: strands of connected keratin proteins, seen through a high-powered microscope.
Complete the sentence.
The mutation in the () affected the structure and function of the ().
A. KRT13 gene . . . keratin protein
B. keratin protein . . . KRT13 gene
From the given choices, select the correct answer and reply with the letter of the chosen option.
Answer: A