Table of ContentsView AllTable of ContentsHow Eye Color DevelopsGenetics and Eye ColorPredicting Eye ColorEye Color and Health
Table of ContentsView All
View All
Table of Contents
How Eye Color Develops
Genetics and Eye Color
Predicting Eye Color
Eye Color and Health
ePhotoAlto / Ale Ventura Collection / Brand X Pictures / Getty Images
The colored part of the eye is called theiris. What we see as eye color is really just a combination of pigments (colors) produced in a layer of the iris known as the stroma. There are three such pigments:
A newborn’s eye color is usually related to their skin tone. White babies tend to be born with blue or sometimes gray eyes. Black, Hispanic, and Asian babies commonly have brown or black eyes.
Are all babies born with blue eyes?Not all babies are born with blue eyes. Contrary to the popular belief that all babies start life with blue eyes, there are many babies born with brown eyes. It can be difficult to predict eye color, but many babies' eyes will turn brown or a darker color within three years after being born.
Are all babies born with blue eyes?
Not all babies are born with blue eyes. Contrary to the popular belief that all babies start life with blue eyes, there are many babies born with brown eyes. It can be difficult to predict eye color, but many babies' eyes will turn brown or a darker color within three years after being born.
Each gene has two different versions (alleles). You inherit one from your mother and one from your father. If the two alleles of a specific gene are different (heterozygous), the dominant trait is expressed (shown). The trait that is hidden is called recessive.
If a trait is recessive, like blue eyes, it usually only appears when the alleles are the same (homozygous).
Generally, darker eye colors are the most dominant.Brown eye color is a dominant trait and blue eye color is a recessive trait. Green eye color is a mix of both. Green is recessive to brown but dominant to blue. Although green eyes are dominant to blue eyes, they are still rarer than other eye colors.
Blue eyes are attributed to a common ancestor shared between every person with blue eyes.
Can Two Blue-Eyed Parents Have a Brown-Eyed Child?It is possible for two blue-eyed parents to have a brown-eyed child. Blue eye color is recessive while brown eye color is dominant. So, if the gene for brown eye color is present in the parents' DNA, then their child could have brown eyes.
Can Two Blue-Eyed Parents Have a Brown-Eyed Child?
It is possible for two blue-eyed parents to have a brown-eyed child. Blue eye color is recessive while brown eye color is dominant. So, if the gene for brown eye color is present in the parents' DNA, then their child could have brown eyes.
Still, the Punnett square chart is not an accurate way to predict more complex problems of inheritance. For example, according to the Punnett square, two blue-eyed parents cannot have a brown-eyed child. However, if two blue-eyed people carry the DNA for brown eyes from their parents, then it is still possible—albeit unlikely—that their child will inherit brown eyes.
Determining each parent’s alleles can be complicated. As a dominant trait, brown eyes can come from six differentgeneticcombinations. They can also hide recessive (hidden) traits of green or blue eye color. To find recessive traits, it’s helpful to know the grandparents' eye colors.
For example, a blue-eyed parent whose entire family has blue eyes and a brown-eyed parent whose mother and father were brown- and blue-eyed has a 50/50 chance of having a blue-eyed or brown-eyed child.
Scientists have begun to develop methods for predicting eye color. They use genetic tests that identify specific polymorphisms (versions of a gene) that can indicate how much melanin, pheomelanin, and eumelanin will be produced.
Waardenburg Syndrome
Heterochromia, in which a person has two different colored eyes, can be a sign that a person hasWaardenburg syndrome. Heterochromia often presents as one blue eye and one brown eye.
Waardenburg syndrome is a genetic condition that can cause hearing loss in one or both ears. People with Waardenburg syndrome may also be born with very pale eyes or one eye that is two colors.
Having multiple colors within the same eye—known as central heterochromia (or tie-dye eyes)—is not associated with health problems.
Ocular Albinism
The gene for ocular albinism is recessive but it is located on the X chromosome. Because men have only one X chromosome, the ocular albinism gene will always be expressed in men who carry it.
Studies suggest fewer than one out of every 60,000 men has ocular albinism.
Aniridia
Summary
16 Sources
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