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.

Some plant proteins control how flowers grow and develop. In Arabidopsis thaliana (A. thaliana) plants, one of these proteins is called ULTRAPETALA1. The ULTRAPETALA1 protein is encoded by the ULT1 gene.
The ULTRAPETALA1 protein allows only a specific number of cells in the growing flower bud to divide and form petals. This results in A. thaliana flowers with four petals.
A certain A. thaliana plant had a mutation in the ULT1 gene that caused the plant to have flowers with six petals instead of four. Compared to the ULT1 gene without a mutation, the mutated ULT1 gene encoded a form of the ULTRAPETALA1 protein with a different structure.
This different form of the ULTRAPETALA1 protein allowed more cells than normal to grow and form petals.
Figure: an A. thaliana flower with four petals.
Complete the sentence.
The mutation in the () affected the structure and function of the ().
A. ULTRAPETALA1 protein . . . ULT1 gene
B. ULT1 gene . . . ULTRAPETALA1 protein
Determine the correct option from the provided choices and reply with its corresponding letter.

B