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Blue Sky Science: Why can eye color vary between siblings?

Holden Taggart

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Why can eye color vary between siblings?

Eye color is determined by genetics and genes can vary between siblings. We all have genes in our body, and our genes carry DNA. Our DNA controls the way that we express different characteristics in our body, everything from hair color to eye color to skin color.

It was thought that there were only a few genes that determined eye color. In more recent years, scientists have realized there are many different genes and factors that affect eye color. In fact, they’ve found up to a dozen or more genes that could play a role in determining eye color.

Two genes that are most important are involved in the production of melanin. Melanin is a pigment, a type of pigment that has a very dark brown or black color.

The amount of melanin expressed in the body, specifically in the eye, determines how dark our eyes are. It can vary from being very light blue to dark brown depending on how much melanin is in the eye.

The specific part of the eye that determines color is called the iris. It’s colored ring that surrounds the pupil, which is the black center of the eye that you look through.

Siblings can inherit various genes from their parents and they don’t always get the same ones. Depending on what genes they get and the way that these genes are turned on or off and expressed, can play a role in eye color. That’s how you’re able to get one sibling with light blue eyes versus another sibling that has dark brown-colored eyes.

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About the Morgridge Institute for Research

As an independent research organization, the Morgridge Institute for Research explores uncharted scientific territory to discover tomorrow’s cures. In affiliation with the University of Wisconsin-Madison, we support researchers who take a fearless approach to advancing human health in emerging fields such as regenerative biology, metabolism, virology and medical engineering. Through public programming, we work to inspire scientific curiosity in everyday life.

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