воскресенье, 20 октября 2019 г.

Why Babies Are Born With Blue Eyes

Why Babies Are Born With Blue Eyes You may have heard that all babies are born with blue eyes.  You inherit your eye color from your parents, but no matter what the color is now, it may have been blue when you were born. Why? When you were an infant, melanin- the brown pigment molecule that colors your skin, hair, and eyes- hadnt been fully deposited in the irises of your eyes or darkened by exposure to ultraviolet light. The iris is the colored part of the eye that controls the amount of light that is allowed to enter. Like hair and skin, it contains the pigment, possibly to help protect the eye from the sun. How Melanin Affects Eye Color Melanin is a protein. Like other proteins, the amount and type your body produces are coded into your genes. Irises containing a large amount of melanin appear black or brown. Less melanin produces green, gray, or light brown eyes. If your eyes contain very small amounts of melanin, they will appear blue or light gray. People with albinism have no melanin in their irises at all. Their eyes may appear pink because the blood vessels in the back of their eyes reflect light. Melanin production generally increases during the first year of a babys life, leading to a deepening of eye color. The color is often stable by about six months of age, but it may take as long as two years to fully develop. However, several factors can affect eye color, including the use of certain medications and environmental factors. Some people experience changes in eye color over the course of their lives. In some cases, people can even have eyes of two different colors. Even the genetics of eye color inheritance isnt as cut-and-dried as was once thought, as blue-eyed parents have been known (rarely) to have a brown-eyed child. Furthermore, not all babies are born with blue eyes. A baby may start out with gray eyes, even if they ultimately become blue.  Babies of African, Asian, and Hispanic descent are more likely to be born with brown eyes. This is because darker-skinned individuals tend to have more melanin in their eyes than Caucasians. Even so, a babys eye color may deepen over time. Also, blue eyes are still possible for babies of dark-skinned parents. This is more common in preterm babies because melanin deposition takes time. Humans arent the only animals that experience eye color changes. For example,  kittens are often born with blue eyes, too. In cats, the initial eye color change is fairly dramatic because they develop so much more quickly than humans. Feline eye color changes over time even in adult cats, generally stabilizing after a couple of years. Even more interesting, eye color sometimes changes with the seasons. For example, scientists have learned that reindeer eye color changes in the winter. This is so that reindeer can see better in the dark. Its not only their eye color that changes, either. The collagen fibers in the eye change their spacing in the winter to keep the pupil more dilated, allowing the eye to capture as much light as possible.

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