The Fun Vision Facts – Part 1 was so much of a hit that I thought a sequel was necessary. Normally I write about serious topics concerning your vision. However, today I’m doing something different. While researching different vision topics, I always run across fun vision facts and answers to questions like do you know why your eyes are baby blue while your brother’s or sister’s are hazel?
Random eye facts:
- Q: “Is it true that if you cross your eyes, they’ll stay that way forever?”
A: No, this is a myth. But please don’t sit so close to the TV!
- About 1.3 million U.S. residents are considered legally blind (American Foundation for the Blind).
- About 25.4% of U.S. residents are nearsighted (myopic) and 9.9% are farsighted (hyperopic), according to the National Eye Institute.
- About 22 million Americans struggle with the painful symptoms of allergic conjunctivitis, also known as eye or ocular allergies.
- A human eyeball weighs an ounce.
- In the United States, approximately 25,000 eye injuries occur that result in the person becoming totally blind.
- The eye of a human can distinguish 500 shades of the gray.
Eye Color – How is it Determined?
Have you ever wondered why your sister has hazel eyes but yours are blue? If you’re expecting, you may be trying to guess your baby’s eye color based on the eye color of grandparents and other family members. Lets take a look at eye color inheritance, which is a bit more complicated than we may have learned in high school. So the next time someone says to you, “You have your mother’s eyes,” you can reply, “Well, I certainly have her alleles.”
Eye color is a physical trait that is determined by the pairing of genes from both parents. Scientists used to think that a single gene pair following dominant and recessive inheritance patterns was responsible for this trait. Now they know there are at least three gene pairs controlling human eye color.
Geneticists have focused on two of the three gene pairs to help clarify the inheritance of eye color: the gey gene and the bey 2 gene. The bey 2 gene, on chromosome 15, has a brown and a blue allele. (An allele is a form of the gene occupying a specific position on the chromosome.) Located on chromosome 19, the gey gene has a blue and a green allele. The third gene, bey 1, located on chromosome 15, is a central brown eye color gene. The brown allele is always dominant over the green and blue alleles, the green allele is always dominant over the blue allele, and the blue allele is always recessive.
If the Blue Allele is Recessive, Why do People Have Blue Eyes?
Blue-eyed folks have inherited a pair of blue alleles from both their mother and their father. That is, blue eyes will occur only if all four alleles are for blue eyes. This is why blue eyes are relatively rare, found mainly in people of northern European descent.
If this child were to get one green allele in the mix, she or he would have green eyes. If a brown allele is present, regardless of what the other three alleles are, the child would have brown eyes, the most common color, predominant in people of Asian and African descent.
Green eyes are found most commonly in people of Celtic, Slavic, and Germanic descent. Interestingly, blue eyes can become green as a person ages, but green eyes can’t become blue.
How do People Get Hazel or Gray Eyes?
The two-gene model cannot account for hazel or gray eyes, nor can it explain how it is possible for two brown-eyed parents to have a blue- or green-eyed child. It also provides no ready explanation for the rich multiplicity of eye shades, from cocoa-colored brown to teal blue to sage green. This suggests the existence of other genes, yet to be discovered, that determine eye color or modify the expression of the known eye color genes. Or perhaps mutations or other factors are also involved in eye color inheritance.
What about People who Have Two Different-colored Eyes?
The condition of having two irises of different colors is called heterochromia iridium, which is a rare hereditary trait. Heterochromia iridium can also be caused by trauma to the eye, or eye diseases and the medications used to treat them (such as that for glaucoma), which increase or decrease the pigmentation of one eye. The musician David Bowie, actress Kate Bosworth, and actor Joe Pesci all have this condition.