Eyes with no melanin on the front layer of the iris scatter light so that more blue light reflects out, so that the eyes appear blue. The chromosomes a child inherits carry genetic information that determines eye color. Differences in the copies received from each parent causes variations in the amount of melanin produced.
A region on chromosome 15 has a big part in determining eye color. The OCA2 gene formerly called the P gene provides instructions for producing the P protein located in the melanocytes specialized cells that produce melanin. If more protein is produced, then the eyes received more melanin, and eye color leans toward the brown end of the color spectrum. When less protein is produced, the eyes receive less melanin and eye color leans toward the blue end of the spectrum.
Although nearly 75 percent of eye color is controlled by the OCA2 gene, other genes provide a pathway for melanin. These genes can raise or lower melanin levels, causing a child to have more or less melanin than either parent.
These variations can result in blue-eyed parents having a brown-eyed child, or brown-eyed parents having a blue-eyed child. The former is more likely than the latter. Each cell in the human body normally contains 23 pairs of chromosomes. Chromosome 15 likely contains to genes integral to producing proteins.
The presence of at least one genetic variation in the HERC2 gene can reduce the amount of melanin produced, leading to lighter eyes.
Eye color was once thought to be the result of a single hereditary trait. It was thought that each person received one eye color gene from each parent, and the dominant gene determined eye color. In this model, the brown-eye color gene was always dominant over the blue-eye color gene, and only two blue-eye color genes could color eyes blue.
Charles and Gertrude Davenport developed the dominant brown eye model in They suggested that blue eyes were caused by a single recessive gene, and blue-eyed parents could never produce a brown-eyed child.
Dominant and recessive genes refer to inheritance patterns, and describe how likely it is for a certain trait to pass from parent to offspring. Today, we know this model is simplistic, and that many genes determine that eye color. While it is possible to predict the probability of eye color, genetic factors may alter the outcome. With eye color controlled by more than one gene, it is possible for a newborn to inherit any eye color.
Predicting eye color is further complicated because it sometimes changes after birth. According to one theory, almost everyone This is based on the DNA analysis of about blue-eyed people, in which only one person did not have the same blue-eye genetic mutation as the rest of the group. This mutation seems to have occurred during the Neolithic period or New Stone Age during the great agricultural migration to the northern part of Europe.
Nearly all blue-eyed humans have this same mutation in the same location in their DNA. By contrast, brown-eyed humans have more variation in their DNA when it comes to eye color.
The majority of people in the world have brown eyes. The color brown is a result of a high concentration of melanin in the iris causing more light to be absorbed and less light to be reflected. Because of this, brown eyes are more naturally protected from the sun.
Blue eyes get their color the same way water and the sky get their blue color. They scatter light so that more blue light reflects back out. The colored part of the eye is called the iris. You can see the iris in action when it squeezes or relaxes to let in more or less light through the pupil. The iris is made up of two layers. For almost everyone — even people with blue eyes — the back layer called the pigment epithelium has brown pigment in it.
The genetics of eye color are very complicated. Even parents who have the same color eyes as each other could have a child with different colored irises. Genetic research has shown that blue eyes probably only appeared in the last 6, to 10, years. Before then, everyone had brown eyes. Blue eyes have probably spread through the population just because some people like how they look and chose to have children with blue-eyed people.
Green and hazel eyes are a mixture of pigment color and color from scattered light, so they can also look different in different lighting conditions. Babies often do not have much pigment in their irises when they are born.
Worldwide, fewer than one in every 10 people sport a blue eye color. Between 6, and 10, years ago, a baby was born in Europe with a harmless genetic mutation. As far as researchers can tell, this was the first person with blue eyes, and everyone who has blue eyes today is a very distant relative of this ancient human.
Eye color depends on how much of a pigment called melanin lives in the iris of the eye. Melanin is also responsible for the color of our skin, eyes and hair. This genetic switch limits how much melanin is produced in the iris — effectively "diluting" brown eyes to a shade of blue. In addition to having significantly less melanin in their iris than people with brown eyes, hazel eyes or green eyes , blue-eyed individuals don't have very much variation in the part of their DNA responsible for melanin production.
The color of our eyes depends on how much melanin is present in the iris. Brown eyes have the highest amount of melanin in the iris, and blue eyes have the least.
Brown melanin is the only pigment that exists in the eye; there is no pigment for hazel or green — or blue. Eyes only appear to be these colors because of the way light strikes the layers of the iris and reflects back toward the viewer. At one time, it was believed that eye color, blue eyes included, was a simple genetic trait. Common knowledge said that you could predict a child's eye color if you knew the color of their parents' eyes, and possibly the color of their grandparents' eyes.
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