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Euclides
Tuesday, May 11th, 2004, 11:27 PM
Phenotypes and Genotypes for human eye colors
Part of the study of genetics involves being able to predict the appearance (phenotype) and genetics (genotype) of the offspring of animals or people. Sometimes this is just for fun, such as breeding dogs to get a certain color, but sometimes it is very serious, as when dealing with diseases that can be passed from parents to their children. Here is an example of what we know about the genetics of eye color.

There are three known human eye color genes named: EYCL1 (gey), the Green/blue eye color gene, located on chromosome 19. EYCL2 (bey1), the central brown eye color gene, possibly located on chromosome 15. EYCL3 (bey2), the Brown/blue eye color gene located on chromosome 15. A role has also been suggested for the Melanocortin Receptor Gene (MCIR) on chromosome 16. A second gene for green has also been postulated. Other eye colors including black, grey, and hazel are not yet explained. We do not yet know what these genes make (except MCIR), or how they produce eye colors. The two gene model (EYCL1 and EYCL3) used here clearly does not explain more than a portion of human eye color inheritance.

Two gene model: There are two genes involved in eye color. One gene has Dominant Brown or recessive blue states, the other has Dominant Green or recessive blue states. We further assume that Brown in the first gene will swamp out Green or blue from the second gene, and Green from the second gene will swamp out blue from the first gene. Because chromosomes come in duplicate pairs, each parent has two copies of each gene.



Phenotypes and Genotypes for human eye colors

Possible Phenotypes and Genotypes under the two gene model

Phenotype: Blue Eyes
1 Possible Genotype:
Gene: bey2 Gene: gey
Chromosome 15 Copy 1: blue
Chromosome 15 Copy 2: blue Chromosome 19 Copy 1: blue
Chromosome 19 Copy 2: blue


Phenotype: Green Eyes
2 Possible Genotypes:
Gene: bey2 Gene: gey
Chromosome 15 Copy 1: blue
Chromosome 15 Copy 2: blue Chromosome 19 Copy 1: Green
Chromosome 19 Copy 2: Green
Chromosome 15 Copy 1: blue
Chromosome 15 Copy 2: blue Chromosome 19 Copy 1: Green
Chromosome 19 Copy 2: blue


Phenotype: Brown Eyes
6 Possible Genotypes:
Gene: bey2 Gene: gey
Chromosome 15 Copy 1: Brown
Chromosome 15 Copy 2: Brown Chromosome 19 Copy 1: Green
Chromosome 19 Copy 2: Green
Chromosome 15 Copy 1: Brown
Chromosome 15 Copy 2: Brown Chromosome 19 Copy 1: Green
Chromosome 19 Copy 2: blue
Chromosome 15 Copy 1: Brown
Chromosome 15 Copy 2: Brown Chromosome 19 Copy 1: blue
Chromosome 19 Copy 2: blue
Chromosome 15 Copy 1: Brown
Chromosome 15 Copy 2: blue Chromosome 19 Copy 1: Green
Chromosome 19 Copy 2: Green
Chromosome 15 Copy 1: Brown
Chromosome 15 Copy 2: blue Chromosome 19 Copy 1: Green
Chromosome 19 Copy 2: blue
Chromosome 15 Copy 1: Brown
Chromosome 15 Copy 2: blue Chromosome 19 Copy 1: blue
Chromosome 19 Copy 2: blue


http://www.athro.com/evo/gen/eyecols.html

Euclides
Tuesday, May 11th, 2004, 11:39 PM
Genetics and determination of iris color
Despite periodical reports of eye color genes "discovered" the iris color remains a highly complex, combined effect of texture, pigmentation and other histological characteristics of an individual's epigenetic constitution. A person's "eye colour" is actually the colour of her or his iris, since the cornea is transparent and the sclera is rarely if ever of any other colour than white. However, the color of the iris results from only one pigment, which is black and only slightly different from melanin in hair and skin for that matter. Sometimes lipofuscin, a yellow "wear and tear" pigment also enters into the net eye color "account", especially in green eyes.

Grosso modo, the physical phenomena described by Tyndall, Raleigh and even Sir Chandrasekhar Venkata Raman, which explain the color of the sky, also explain preferential dispersion of light in the iris. Constructive interference, like in the feathers of birds, has a place in the physical theory. This, as well as full understanding of physical and constitutional characterics of the iris stroma, especially in the anterior border layer cannot be left aside in explanations of iris color. For instance, like in eye spots of butterfly wings, the same chemical component of a given color can yield dramatically different physical components of color depending only of angles of view. Last, but not least, melanin in the iris stroma is maintained in highly mobile and perfectly controlled melanosomes which radically change the diffraction pattern for light entering the iris. In conclusion, reported EYCL3 (Eye color 3 - Brown/Blue Eye Color on HC-15) and EYCL1-GEY (Eye Color 1 - Green/Blue Eye Color on HC-19) are only obvious misnomers, wishful thinking or both.

http://en.wikipedia.org/wiki/Iris_(anatomy)