Phenotype and genotype studies
To address the challenge of achieving good predictability of laser iridoplasty, we first had to clarify the scientific bases that determine the color of the eyes. The fundamental law is genetic and it is the Theory of the two genes, green and blue (Figure 6). The first thing to notice about this table is that when there is a B, the eyes turn brown. So B is dominant over G and b. In addition to that, when there is a G (but not B), the eyes turn green. Then, G is dominant over b. Some of these details must seem a bit strange. First, there are two distinct genes, but B of one gene is dominant over G of the other gene. The other strange thing is that the recessive form of both genes is blue.These two things are related. The eye color corresponds to the amount of melanin pigment in the eye. Not anywhere in the eye, but in a special place, the stroma of the iris. A lot of melanin in this part of the eye results in brown eyes and less melanin results in green eyes. Little melanin or the absence of melanin in the stroma of the iris results in blue eyes. For this reason the brown color is dominant over the green color. Version B of OCA2 tells the eyes to produce a lot of melanin. The G version of the gey gene tells the eye to produce some melanin. What happens if both genes are present? A lot of melanin is produced and this results in brown eyes. The fact that the recessive form of both genes is blue makes sense. The recessive form of both genes does not work and that thus it is recessive. An OCA2 gene without function is equal to a gene without function (melanin does not occur in the stroma).
The absence of melanin in the stroma results in blue eyes. Now we can understand why brown is dominant over green. And
why blue is recessive to both.