Answer:
b. Gene expression
Step-by-step explanation:
The eye color trait is controlled by polygenetic heritability. A group of genes is responsible for the trait manifestation, and they must be associated to transmit the characteristic.
Eye color in a person is produced by pigments in the iris´ cells called melanocytes. At least two or more genes control melanin synthesis in the iris. Melanosomes are cellular structures produced by melanocytes, where melanin is produced and stored. Different genes control the eye color by its expression. We can name two of them as examples. There is a gene called OCA2 that codifies for the P protein synthesis. This protein plays an important role in the amount of melanin produced. The less P protein, the less melanin the cell will produce, which leads to blue eyes. Another gene called HERC2 contains a region known as intron 86 that controls the OCA2 gene, by allowing or inhibiting its expression.