Re: What genes or how many gene pairs cause a specific eye color.

Dear Stan,

Eye color is still believed to be a polygenic trait. However, genes have been mapped that show single-gene patterns of inheritance for green/blue and brown eyes (via the database of Online Mendelian Inheritance in Man)

BEY: Brown eye color. Certain families show linkage of the brown eye color to other genetic markers on chromosome 15. Though melanin is known to be the iris pigment producing the color, is it now yet known what the function of the BEY gene is (transport, controls expression of melanin, etc..). BEY1 is the genetic locus associated with the phenotype of a completely brown or centrally brown iris.

GEY: Green eye color. This locus has tentatively been mapped to chromosome 19, and is believed to be heterogeneous in nature (with more than 2 alleles). The blue/green phenotype may also involve more than the single GEY locus. The function of the GEY locus is not known.

How the BEY/GEY genes interact to produce a given eye color is still not clear, even when regarding the dominance of one color over another (brown over green/ blue, for instance). To quote the GEY entry:

Eye color is likely to be a polygenic trait. The early view that blue is a simple recessive has been repeatedly shown to be wrong by observation of brown- eyed offspring of 2 blue-eyed parents. My monozygotic twin brother and I, brown- eyed, had blue-eyed parents and blue-eyed sibs. Blue-eyed offspring from 2 brown-eyed parents is a more frequent finding. In some Norwegian families, Gedde-Dahl (1981) found diffusely brown eyes or centrally brown eyes segregating as simple dominant traits, symbolized BEY1

Hope this helps..

-L. Bry, MadSci Admin