The Genetics of Eye Color


** The Genetics of Eye Color **

** Linda Claire Guttery **

Student Projects,Color


** Introduction **

How do children inherit eye color? Can a child's eye color be predicted?
Why are an albino's eyes pink? How can two brown eyed parents produce a
blue eyed child? Why are my eyes a darker blue than my sibling's? How are
the colors in the iris formed? These are questions one may have wondered
from time to time. The answer to all of these question lies in the genes
inherited from a one's parents.

** Background **

Different eye colors are produced because of the different amounts and
patterns of pigment in the iris. The amount of pigment and the pattern of
the pigment is determined by a person's genetic makeup. The DNA received
from one's parents determines what color eyes they will have.

Each human has 46 chromosomes located in the nucleus of the cell. These are
divided into 23 pairs of chromosomes. A baby inherits one chromosome from
each parent in each pair of chromosomes. A piece of DNA on a chromosome is
called a gene. Genes are the basic unit of heredity, they determine many
characteristics about a baby. Genes also come in pairs. Alleles are found
in genes and determine the appearance of any characteristic. There are two
alleles for each trait inherited. If the two alleles are the same then they
are homozygous for that gene. If the alleles are different, then they are
called heterozygous. One allele is expressed over the other allele. This is
called the dominant allele, the unexpressed allele is called recessive. For
example, if there was a brown allele and a blue allele, the brown is
dominant, so the person would have brown eyes. But


how is eye color determined

Eye color - Wikipedia, the free encyclopedia


** Eye color **

From Wikipedia, the free encyclopedia
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Close up of a human iris
Map of the distribution of the light eyes(Blue, Green and Gray) in Europe
at the middle of the 20th century by the American anthropologist Carleton
S. Coon
Another map showing the distribution of light eyes(Blue and Green) and dark
eyes(Brown and Black) in Europe

*Eye color* is a polygenic phenotypic character determined by two distinct
factors: the pigmentation of the eye's iris^[1]^[2] and the
frequency-dependence of the scattering of light by the turbid medium in the
stroma of the iris.^[3]

In humans, the pigmentation of the iris varies from light brown to black,
depending on the concentration of melanin in the iris pigment epithelium
(located on the back of the iris), the melanin content within the iris
stroma (located at the front of the iris), and the cellular density of the
stroma.^[4] The appearance of blue, green, as well as hazel eyes results
from the Rayleigh scattering of light in the stroma, a phenomenon similar
to that which accounts for the blueness of the sky. Neither blue nor green
pigments are ever present in the human iris or ocular fluid.^[3]^[5] Eye
color is thus an instance of structural color and varies depending on the
lighting conditions, especially for lighter-colored eyes.

The brightly colored eyes of many bird species result from the presence of
other pigments, such as pteridines, purines, and carotenoids.^[6] Humans
and other animals have many phenotypic variations in eye color.^[7] The
genetics of eye color are complicated, and color is determined by multiple
genes. So far, as many as 15 genes have been associated with eye color
inheritance. Some of the eye-color genes include


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