A 13 year old male patient complains about the discoloration of his teeth. His mother shows a similar discoloration of her teeth. Clinical findings reveal teeth with mottled, opaque white brown yellowish discoloration. Snowcapped appearance of teeth is appreciable. OPG reveals a thin layer of enamel over the cusp tips and interproximal surfaces. Probe test is positive. Based on the Pedigree chart for the inheritance of this disorder, which of the following gene may be affected?