Blue-eyed parents can have brown-eyed kids and other eye-oddities
Both my wife and I have brown eyes. My son was born with brown eyes. However,
they turned blue within two weeks. Is this common? Mike,
New York, New York
Can two blue-eyed parents produce a child with dark brown
eyes? Sara, Medford, Oregon
If both parents have brown eyes, can they have a child with
blue eyes? Frederick, Atco, New Jersey
 Where genes live: An idealized DNA molecule (which dwells
in the nucleus of a cell). A gene is a piece of the DNA molecule that determines
a particular characteristic — like height. [NASA]
No, Mike. It is uncommon for a Caucasian baby to be born with brown
eyes. Almost all such babies have blue eyes because the iris has not yet made brown
pigment (called melanin) that colors the iris. It is, however, common for babies
to have blue eyes at 2 weeks. Usually, the iris doesn’t make enough melanin
until about 3 years of age.
Yes, Sara. Two blue-eyed parents can have a child with brown
eyes.
Most of us learned the model for determining eye color that
G.C. Davenport and C.B. Davenport devised in 1907. The Davenport model wrongly
says brown eye color is always dominant over blue eye color, which means that
two blue-eyed parents always have blue-eyed kids. We know better now.
"Although not common, two blue-eyed parents can produce
children with brown eyes," says
Richard A. Sturm , a Principal Research Fellow at the Institute for Molecular Bioscience at the
University of Queensland in Brisbane, Australia.
Eye color is a complex trait that depends on the state of
several interacting genes. The gene that usually decides the issue (blue eyes or
brown eyes) is the OCA2 gene on chromosome 15. But it comes in different
strengths. A person with a weak form of the OCA2 gene will have blue eyes.
Likewise a person with a strong form will have brown eyes.
The plot thickens, though, because an individual also has
other eye-color genes that each has a say in the final eye-color outcome. For
example, if one of these lesser genes is strong, it can make the weak form
(blue) of OCA2 work much more effectively — almost like the strong form (brown).
Then the eye color may be a light brown or muddy grey. In fact, the resulting
color can be any shade of brown, hazel/green, or blue depending on the strengths
of the interactions.
Yes, Frederick. Two brown-eyed parents can have a blue eyed
child. In fact, this is fairly common.
Further Reading:
WonderQuest: When and why a newborn’s eye color changes
Molecular genetics of pigmentation by Rick Sturm, Institute for Molecular
Bioscience, University of Queensland
Ask a
geneticist: eye color
My eyes change colors from blue
to green to gray depending on what I’m wearing. What causes that?
Jennifer, Greenville, Missouri
My eyes change color, constantly: from green to grey to
orange to brown, changing even when I’m upset. It must have a genetic
explanation but what is it? Sara, Los Angeles, California
What causes a person’s eyes to change color frequently?
Mine are hazel... a greenish hue for the most part, but some grey and blue.
Those are the colors they switch to. Someone told me it doesn't have anything to
do with genetics. But rather something else? Siobhan, USA
Ah, we can explain this eye-color change that depends on
the color that you’re wearing, the color of the light that’s shining on your
eyes, or your emotions. It isn’t genetics. It’s light optics.
Suppose
you’re wearing a green shirt, Jennifer. Light hits the green shirt and reflects
the color green off the shirt. That’s why the shirt looks green. Some of the
green light from the shirt also reflects into your eyes. Your eyes then reflect
the green light like a still pool reflects green trees and that makes your eyes
appear green.
 Blue eyes can take on other colors from reflected light
[Corel]
Eye color also depends on the incident light because the eyes
can only reflect colors present in the light shining on them. An incandescent
bulb, sunlight, fluorescent light, or candlelight all produce different
reflected light because their color content differs. Candlelight is deficient in
blue; its light is yellowish. So candlelight shining on hazel eyes will make the
eyes appear more yellow.
Emotions may change eye color by dilating the pupils (for
example, when surprised or angry), says
Brian DeBroff,
ophthalmology professor at Yale University. This wider opening allows more even
red glow to shine forth from the retina (what photographers call "redeye" and
physicians call "red reflex"). The reflected red light could affect eye color.
So it’s no wonder that light eyes can change color frequently
during the day — depending on what we wear, what light we see by, or what
emotion is playing tricks with our eyes.
Further Reading:
WonderQuest: Why blue eyes are blue
What exactly are hazel eyes,
and what color are they? WonderQuest
HyperPhysics by
Rod Nave: Light and vision
(Answered Oct. 15, 2004)
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