How is hair and eye color determined

People with Waardenburg syndrome may also be born with very pale eyes or one eye that is two colors. Very pale blue eyes may be caused by ocular albinism. This is when there is absolutely no pigment in the iris. As an X-linked recessive disorder , ocular albinism occurs almost exclusively in men. This is because men have one X and one Y sex chromosome. The gene for the condition is on the X chromosome.

So, in men, the gene for the condition will be expressed even though it's recessive. Women, on the other hand, have two X sex chromosomes, so they may be carriers. They may have one gene for ocular albinism that is hidden by another normal gene. So they may not have the condition themselves but be able to pass on the gene for it. Studies suggest fewer than one out of every 60, men has ocular albinism.

A baby also may be born missing all or part of their iris, a genetic condition known as aniridia. It's caused by mutations in the PAX6 gene. This gene plays an important role in forming tissues and organs during an embryo's development. Your baby's eye color is determined by genetics. Eye color is a combination of pigments produced in the stroma.

Brown eyes have more melanin than green or hazel eyes. The mix of genes inherited from each parent determines which pigments are produced and the baby's eye color. These genes can also lead to certain conditions. While understanding the genetics of eye color can help you understand how likely a baby will have a certain eye color, there are no certainties.

If you have any questions about your child's eye color or overall eye health, bring your concerns to their pediatrician. Sign up for our Health Tip of the Day newsletter, and receive daily tips that will help you live your healthiest life. American Academy of Pediatrics: HealthyChildren. Newborn eye color. Updated June 8, Is eye color determined by genetics? Updated June 23, Novel quantitative pigmentation phenotyping enhances genetic association, epistasis, and prediction of human eye colour.

Sci Rep. Grigore M, Avram A. Iris color classification scales - then and now. Rom J Ophthalmol. American Academy of Ophthalmology. Your blue eyes aren't really blue. Hazel eyes come from the same combination, but they have more melanin concentrated in the outer top layer of the iris.

Red and violet eyes, which are much rarer, come from a minute to complete lack of pigment. The two genes currently thought to be most strongly associated with human eye color are OCA2 and HERC2, which are both located on chromosome OCA2, the gene we used to think to be the sole player in eye color, controls the production of the P protein and the organelles that make and transport melanin.

Different mutations in this gene act as a switch that turns OCA2 on and off and determines how much P protein it encodes. Those are just the two genes we know about in detail so far. Newer studies have linked as many as 16 genes to eye color , all of which pair with OCA2 and HERC2 to generate a spectrum of different iris colors and patterns. Norton notes that most of what we know about the complicated genetics of eye color, we know through genome-wide association studies GWAS , which track visible traits in subjects with varying DNA profiles.

To date, eight genes have been identified which impact eye color. OCA2 produces a protein called P-protein that is involved in the formation and processing of melanin. Individuals with OCA2 mutations that prevent P-protein from being produced are born with a form of albinism.

These individuals have very light colored hair, eyes and skin. Non-disease-causing OCA2 variants alleles have also been identified. The allele that results in high levels of P-protein is linked to brown eyes. Another allele, associated with blue eye color, dramatically reduces the P-protein concentration.

However, while about three-fourths of eye color variation can be explained by genetic changes in and around this gene, OCA2 is not the only influence on color. A recent study that compared eye color to OCA2 status showed that 62 percent of individuals with two copies of the blue-eyed OCA2 allele, as well as 7. An abundance of another pigment, called pheomelanin, gives people red hair. The type and amount of melanin in hair is determined by many genes, although little is known about most of them.

The best-studied hair-color gene in humans is called MC1R. This gene provides instructions for making a protein called the melanocortin 1 receptor, which is involved in the pathway that produces melanin.

The melanocortin 1 receptor controls which type of melanin is produced by melanocytes. When the receptor is turned on activated , it triggers a series of chemical reactions inside melanocytes that stimulate these cells to make eumelanin. If the receptor is not activated or is blocked, melanocytes make pheomelanin instead of eumelanin. Many other genes also help to regulate this process. Most people have two functioning copies of the MC1R gene, one inherited from each parent. These individuals have black or brown hair, because of the high amount of eumelanin.

It is estimated that more than 90 percent of people in the world have brown or black hair. Some people have variations in one copy of the MC1R gene in each cell that causes the gene to be turned off deactivated.

This type of genetic change is described as loss-of-function. For these individuals, eumelanin production is lower, while pheomelanin production is higher, so they have strawberry blond, auburn, or red hair. In an even smaller percentage of people, both copies of the MC1R gene in each cell have loss-of-function changes, and the melanin-production pathway produces only the pheomelanin pigment. The hair of these individuals is almost always very red.

Even when the melanin-production pathway is making eumelanin, changes in other genes can reduce the amount of eumelanin produced. These changes lead to blond hair.