top-rated free essay

How is Eye Color Inherited?

By bk1212 Jul 26, 2013 1440 Words
How is Eye Color Inherited?

How do children inherit eye color? Can a child's eye color be predicted? Why are an albino's eyes pink? How can two brown eyed parents produce a blue eyed child? Why are my eyes a darker blue than my sibling's? How are the colors in the iris formed? These are questions one may have wondered from time to time. The answer to all of these questions lies in the genes inherited from a one's parents. Blue eyes are found only in people with European ancestry. The widespread nature of blue eyes in these populations suggests that it was a trait that was somehow selected for after it arose. But there is no known advantage to having blue eyes. In fact, some eye diseases, such as uveal melanoma (the most common eye cancer in adults) and Age-related Macular Degeneration, are more common in people with lighter eyes. The lower rate of such diseases in people with darker eye colors may be due to the protective effects of eumelanin in darker eyes. Just as melanin helps protect skin against UV damage from the sun, melanin may also protect cells in the back of the eye that are important for vision. According to (Frudakis, 2004)Because blue eyes don't offer an advantage when it comes to dealing with the environment, some scientists have posited that blue eyes stuck around simply because people with blue eyes were considered more desirable mates. This may be an example of what scientists call "frequency dependent selection" where individuals with rare traits are considered more attractive Different eye colors are produced because of the different amounts and patterns of pigment in the iris. The amount of pigment and the pattern of the pigment are determined by a person's genetic makeup. The DNA received from one's parents determines what color eyes they will have. Each human has 46 chromosomes located in the nucleus of the cell. These are divided into 23 pairs of chromosomes. A baby inherits one chromosome from each parent in each pair of chromosomes. A piece of DNA on a chromosome is called a gene. Genes are the basic unit of heredity; they determine many characteristics about a baby. Genes also come in pairs. Alleles are found in genes and determine the appearance of any characteristic. There are two alleles for each trait inherited. If the two alleles are the same then they are homozygous for that gene. If the alleles are different, then they are called heterozygous. One allele is expressed over the other allele. This is called the dominant allele; the unexpressed allele is called recessive. But not just one pair of genes can control a single trait. Right now there are three known gene pairs that control eye color. The bey 2 gene on chromosome 15 contains a brown and blue allele. Also on chromosome 15, the bey 1 gene is the central brown gene. On chromosome pair 19 the gey gene contains a green allele and a blue allele. A green allele is dominant over a blue allele, and a brown allele is dominant over both green and blue alleles. For the bey 2 genes if a person has a brown allele then they will have brown eyes. In the gey gene the green allele is dominant over the blue allele, but it is still recessive next to a brown allele. According to (Amram., 1939) if a person has a brown allele on chromosome 15, but all the other alleles are blue or green, they will have brown eyes. A green eyed person would have a green allele on chromosome 19 and all or some other blue alleles. Blue eyes are produced only with two blue eye genes. All four alleles must be blue to produce a blue eyed person. Another way of predicting the color of a child's eyes is to use the parent's eye color genes. If both parents have a blue and brown gene, their eyes are brown, but if the child inherits the blue gene from each parent then the child will have blue eyes. If the child only inherits one blue gene then they will have brown eyes. The genetics determine what color a child will have, but how exactly does this color form in the eye? Melanin, a pigment also found in the skin, is the substance that produces the eye colors specified by the genes. The amount and placement of the melanin produces the different eye colors that we see. Melanin is a dark brown pigment that is placed in the iris. The more melanin used in the iris means the darker the eye color will appear, the less melanin used means that the eye color will be lighter. There are actually two types of melanin. Eumelanin is a blackish-brown pigment, while pheomelanin is reddish-yellow. Both types of melanin are contained in tiny granules within skin, hair, and eye cells. The genes tell the enzymes how much melanin to deposit in the iris. A newborn's eyes appear blue, but may darken over the next few years. Melanin production has not begun at the time of birth. A child's true eye color cannot be determined until the age of three. There are two layers to the iris, the anterior and the external, or front and back layers. To produce blue eyes, there is no pigment found in the front layer. The brown pigment melanin is deposited in the back layer only. It appears blue because of reflection and diffraction of light. In green eyes, a small amount of melanin is deposited in the front layer of the iris along with the melanin found in the back layer. The additional pigment to the amount needed for blue eyes, causes the eye to appear green. To produce gray eyes, the dark pigment is distributed in the front layer of the iris and over the blue background it appears gray. In brown eyes there is so much pigment in the front layer, that the blue behind is completely covered up. Some people have so much pigment in the front layer that their eyes appear very dark brown or black. Hazel, blue-green, gray-blue eye colors are produced by different amounts of pigmentation and the pattern in which the pigment is placed. Albino eyes are having no pigment at all in either layer of the iris. The iris appears pink or red because of the reflection of blood vessels in the back of the eye. The pattern in which the pigment is deposited is also determined by genetics. The pigment may be deposited in rings, clouds, radial stripes, or spread over the entire iris. (Clyde, 1999) Say’s if a person has two different eye colors this is called heterochromia. This is considered abnormal and may be pathological. If a person has always had two different colored eyes, then this is called congenital heterochromia and is cause by a difference in the early stages of development of the iris. This is rare, but nothing to have medical concern over. If the heterochromia is acquired after time then there is reason to believe that something has happened within the body to create changes in melanin synthesis or degradation. This can be caused by diseases in the eye or by certain types of medicines. You may have noticed that on certain occasions, your eye color looks different. Is it changing? Not really. The eye color you observe in yourself or another person is due to the interaction of light with the eyes. That means that the eye color you perceive can change depending on the lighting conditions. But the melanin content of adult eyes doesn't change. One exception is that some glaucoma medications can actually cause eyes to become darker. Babies' eyes can change color. Many infants are born with blue eyes that then darken during their first year of life. This happens because the melanin in the outer layers of their irises takes a while to build up. A person's eye color is determined by the genes inherited from their parents. The types of alleles received from the parents are assigned to certain chromosomes. The dominant genes are expressed and the recessive genes are hidden. In the development of the iris those genes tell enzymes to produce and place a certain amount of melanin in the iris to form the eye color.

Works Cited
Amram., S. (1939). You and Heredity. New York: Frederick A. Stokes Company, . Clyde, O. (1999). The Human Eye: Structure and Function. Sinauer Associate Inc. Frudakis, S. a. (2004). Eye Colour: Portals into Pigmentation genes and ancestry. Trends Genet.

Cite This Document

Related Documents

  • eye color genetics

    ...discussing whether or not eye color is genetic. According to dictionary references, genetics is “the science of heredity, dealing with resemblances and differences of related organisms resulting from the interactions of their genes and the environment” (The Free Dictionary). This means that when it comes to humans each physical characteristi...

    Read More
  • Eye Color and House

    ...wobbly steps and stepped inside the doorway. ‘Wow’ the inside of the house… was beautiful ! It was just like the rest of the houses in the town. I thought it would have creaky floorboards and grey brick walls or something. “Come down the hallway” The voice called out interrupting my thoughts “Okay, coming” I answered. I slowly made...

    Read More
  • Eye Color and Olivia

    ...Diana is a creative 32 year old chef. Her hair the color of red maple leafs that layer the dew covered ground in fall. Loose day old curls fall to her shoulders, pulled back and held up with a yellow ribbon secured with a bow. Smells of light jasmine and fresh linen came from her navy blue and white floral knee length dress that permeates the s...

    Read More
  • Accused: Eye Color and Man

    ...arched up into the air and its paws held up as if ready to leap, whether to strike or flee. “Ashes, ashes.” A small drizzle started to fall from the gray clouds outside. Fat rain drops thumped gently against the wooden door. The man placed the rat on the window sill, the heavy stains of dirt working as a sufficient background of his new ma...

    Read More
  • How Colors Affect Emotions

    ... The Effect of Colors and Color Combinations on the Moods of Humans Leon Miguel G. Gonzales Can Color really affect our mood? Introduction: I am curious about the effect of colors and color combinations to people. How do we react to the colors we see? How do we interpret what feeling it gives and can we cure ment...

    Read More
  • How Are We Influenced by Color

    ...Topic: How are we influenced by color? Color is brightness and variety in something, such as a room or picture that gives it interest or immediacy. Color has been known to influence people’s psychological behaviors and associations with iconic objects or ideas. Dark colors are often associated with a somber attitudes, cold places, and even ...

    Read More
  • How the Color of the Rainbow Came to Be

    ...Hour 2 A.P. prep English Rough Draft #5 How the colors of the rainbow came to be…. There once was a village way up in the sky filled with grownups and children who knew how to fly.They were happy and magical and just full of glee and lucky for us they made the rainbow come to be. RED One day Sally was eating a red popsicle and the sun ...

    Read More
  • How to Color Hair.

    ...09/26/11 Intro to Speech. How to dye your own hair. At our age, finding that one gray hair can be quite disturbing. If you dont have any yet, between the stress from school and work, and our entry into adult hood its bound to happen. Thankfully, there are cosmetic products that can help us cover our evidence of old age and k...

    Read More

Discover the Best Free Essays on StudyMode

Conquer writer's block once and for all.

High Quality Essays

Our library contains thousands of carefully selected free research papers and essays.

Popular Topics

No matter the topic you're researching, chances are we have it covered.