The Eye Color Gene: How Genes and Melanin Affect Eye Color
Updated on March 18, 2024
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The Eye Color Gene: How Genes and Melanin Affect Eye Color
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Key Takeaways

Eye color is mainly determined by the type and amount of pigment in the irises called melanin. The genetic makeup of someone’s parents also heavily contributes to eye color.

The genetic variations that control the production, distribution, or concentration of melanin play a role in determining an individual’s eye color.

Whether a person has blue eyes or brown eyes is more than just the simple Mendelian inheritance model.

Mendel’s Laws explain how people inherit traits from their parents.

The first law says that parents give one copy of a trait to their children. These copies split apart when making new generations.

The second law says that different traits are inherited independently. You can get a mix of traits from your parents.

These laws help scientists understand how traits like eye color are passed down from one generation to the next.

While Mendel’s laws suggested a simple dominant-recessive relationship between brown eyes and blue eyes, modern research has found a complex relationship. It found the interaction between multiple genes (polygenic) and factors contribute to the diversity of eye colors.1

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How Do Genes Determine Eye Color?

Genes determine eye color through their influence on melanin production, distribution, and concentration in the iris.

The primary pigments involved are eumelanin (brown or black) and pheomelanin (red or yellow).

The complex genetic process involved in determining eye colors involves the following factors:

Variations in Melanin Production

Genes dictate the production of melanin, the pigment responsible for eye, skin, and hair colors. Variations in specific genes, such as Oculocutaneous Albinism II (OCA2) and HECT And RLD Domain Containing E3 Ubiquitin Protein Ligase 2 (HERC2), impact the amount of melanin produced.

Interaction of Different Genes

Multiple genes define if a person will have blue eyes or other colors. In addition to OCA2 and HERC2, other genes like ASIP, IRF4, SLC24A4, SLC24A5, SLC45A2, TPCN2, TYR, and TYRP1 play roles in melanin production and distribution.2 These genes interact with each other in complex ways to create a selection of eye colors even as rare as green eyes.

Expression and Regulation of Genes

Some genes control the expression of other genes. For instance, HERC2 regulates the activities of OCA2. The discrepancies in gene regulation can influence gene expression. As a result, it can alter melanin production, leading to people having blue eyes or brown eyes.

Melanin Concentration

The balance between eumelanin and pheomelanin can affect eye color. Brown eyes have more eumelanin, while blue eyes and green eyes have less eumelanin and more scattering of light due to the lack of pigmentation.

Inheritance patterns

While simple Mendelian inheritance patterns can help determine eye color, the complexity arises from the fact that multiple genes are involved. Eye color inheritance doesn’t follow a strict dominant-recessive pattern, allowing for a wide range of possible results.

Population and Ancestry

Different populations have a range of combinations of genetic variants that influence eye color. People’s eye color can be affected by their genetic heritage and the diversity of genes in their ancestral backgrounds. Coming from a specific ancestry can usually help determine whether someone will have brown eyes or not.

Environmental Factors

Lighting conditions can influence how eye color is perceived. Eye colors might appear slightly different under different lighting conditions. Blue eyes may appear lighter in a different environment.

Which Genes are Responsible for Different Eye Colors?

Multiple genes contribute to producing different eye colors among humans. Variations in these genes can influence melanin production, transport, and concentration. Therefore, various genetic discrepancies can produce blue, brown, or green eyes.

What are the Known Eye Color Genes?

Eye color is polygenic. Multiple genes involved can influence this trait, including:

  • OCA2 – This is involved in the production and storage of melanin. Certain variations can result in differences in melanin levels, affecting the overall color of a person’s eyes.
  • HERC2 – It is closely related to the OCA2 gene and affects its expression. Variations in the regulatory region of HERC2 impact the activity of OCA2, influencing the amount of melanin produced and, consequently, eye color.
  • Agouti Signaling Protein (ASIP) – It is involved in producing pheomelanin, the red or yellow pigment. Variations in ASIP can affect the balance between eumelanin and pheomelanin, influencing eye color.
  • Interferon Regulatory Factor 4 (IRF4) – Variations in IRF4 can impact melanin levels, which is instrumental to differences in eye color.
  • SLC24A4 and SLC24A5 – They aid in transporting ions needed for melanin production. Discrepancies in these genes can change the type and amount of melanin in the iris.
  • SLC45A2 – It gives specific instructions for making a protein in specialized cells called melanocytes. These cells produce melanin, giving skin, hair, and eyes color.
  • Tyrosinase (TYR) and Tyrosinase-Related Protein 1 (TYRP1) – They have major roles in melanin synthesis. TYR and TYRP1 variations can influence eumelanin and pheomelanin levels, leading to different eye colors.
  • Two Pore Segment Channel 2 (TPCN2) – It can modify the transport of ions needed for melanin synthesis.

How Do Mutations Influence Eye Color?

Genetic mutations can influence eye color by affecting melanin production, distribution, and regulation. Changes in the DNA sequence of a gene can lead to variations in the amount and type of melanin in the iris.

Here’s how genetic mutations can lead to unique eye shades and patterns:

  • Disruption of gene function – Mutations can disrupt a gene’s normal function. The disruption can lead to changes in melanin’s production, transport, or storage, affecting eye color.
  • Change in melanin production – Mutations in genes like TYR and TYRP1 can modify melanin synthesis, leading to variations in the amount and type of pigment produced.
  • Change in the regulatory region – HERC2 mutation can influence gene expression. The mutation can have an effect on the OCA2 gene, which in turn affects melanin production and eye color.
  • Variations in melanin type – Mutations can alter the balance between eumelanin and pheomelanin. ASIP mutation can influence the ratio of these pigments, leading to modifications in eye color.
  • Heterochromia – This is a condition where a person has different-colored eyes. For example, instead of having two blue eyes, a person can have one blue and another dark brown. Heterochromia can be due to variations in the expression of eye color genes in each eye.
  • Rare genetic conditions – Some mutations lead to rare genetic disorders like ocular albinism, where severely reduced pigmentation in the iris leads to very light-colored eyes. These mutations affect genes crucial for melanin production and storage.

Are There Specific Genes for Blue or Brown Eyes?

There are no specific genes exclusively responsible for producing blue eyes or brown eyes.3 Eye color is a polygenic trait, which means multiple genes interact and can affect its outcome.

While certain genetic variations, especially those that handle melanin processes, these genes collectively contribute to a wide range of eye colors.

The intricacy of eye color determination involves the relationship of multiple genes, their variations, and regulatory elements. Many factors are in play that contribute to the diversity of human eye colors.

How is Eye Color Inheritance Understood?

Eye color inheritance can be understood through navigating the relationship among multiple genes, their variations, and complex interactions.

In the traditional sense, understanding eye color inheritance in the simple Mendelian trait says one gene dominates another. However, this has evolved into a more intricate model that accounts for the involvement of multiple genes.

How Do Parents Influence a Child’s Eye Color?

Parents have an effect on their child’s eye color through a combination of genetic interactions and variations. 

Two blue-eyed parents may have a child with blue eyes, but not every time. Sometimes, the kid can end up with brown eyes. Still, the mother and father contribute to their offspring’s final eye color.

It is a common misconception that one parent may strongly influence their kid’s eye color. However, the genetic makeup of both affects their child’s final eye color outcome.

Consequently, predicting the exact eye color of a child can be challenging due to the complex interaction of multiple genes, regulatory mechanisms, and genetic diversity from both parents. Hence, two blue-eyed parents don’t automatically have a kid with blue eyes.

Why Do Some People Still Have Different Eye Colors From Both Parents?

Some people can have different eye colors from both parents due to the complex nature of eye color inheritance.

While the basic Mendelian inheritance model suggests a direct dominant-recessive pattern, the reality is more complicated.

Eye color is influenced by multiple genes. It’s not a simple dominant-recessive pattern like the Mendelian inheritance model.

Therefore, multiple genes can have an effect on the outcome. The final eye color can be tricky to predict with more genes involved.

Genetic mutations and variations from past generations can also result in a person’s unexpected eye color. It means parents with blue eyes can still have a brown-eyed child.

Eye Color and Genetic Conditions

Eye color can sometimes be linked to specific genetic conditions. Some of these conditions include:

  • Albinism
  • Waardenburg syndrome
  • Heterochromia
  • Horner’s syndrome
  • Piebaldism

How is Albinism Related to Eye Color?

People with albinism, a genetic disorder affecting melanin production, often have light-colored eyes due to the lack of pigmentation. Moreover, they have light or white hair and skin.

Are There Other Genetic Diseases That Affect Eye Color?

In addition to albinism, other genetic diseases can affect eye color. These are:

  • Waardenburg syndrome – This is a genetic condition that affects eye color, including striking light blue or differently colored eyes. It is caused by mutations in specific genes that affect pigmentation.
  • Heterochromia – While not a disease, heterochromia is a medical condition where a person has two different eye colors. It can be due to genetic variations or factors like eye injury, surgery, or medications.
  • Horner’s syndrome – This neurological disorder can result in differences in pupil size, impacting the perception of eye color.
  • Piebaldism – A genetic disorder that produces a white forelock of hair, patches of skin without pigmentation, and light-colored eyes.

Common Questions About Eye Color

How Common Is Each Eye Color?

Eye color distribution varies across different regions and populations. However, brown eyes are the most common in the world.4

Let’s take a look at the estimate below on how common is each eye color:

  • Brown eyes – 70 to 80%
  • Blue eyes – 8 to 10%
  • Hazel eyes – 5%
  • Amber eyes – 5%
  • Gray eyes – 3%
  • Green eyes – 2%

Can Eye Color Change Over Time?

Eye color can change over time due to genes, trauma, disease, or medication.5

Eye color change is more likely to happen in childhood. Newborn babies usually have bluish-gray eyes due to the lack of pigmentation. As the amount of melanin in their irises increases, eye color change can happen. Later on, their eyes gradually become darker as they age.

While most people’s eye color becomes stable and permanent by around the age of 6, some may experience subtle changes in their eye color throughout their lives.

How Can I Predict My Baby’s Eye Color?

Since genetics contribute to determining eye color, predicting a baby’s eye color can be tricky. While an educated guess can be made based on the parent’s eye color history, the answer isn’t absolute.

It is essential to understand basic inheritance patterns. Generally, brown eyes are dominant over blue eyes, and green eyes or hazel eyes can result from a combination of genes.

Genetic diversity can lead to unexpected variations. Therefore, a baby’s eye color might follow a complex pattern.

What is the Rarest Eye Color?

Green is the rarest eye color.6 Only 2% of the world’s population has this color.

The unique combination of the amount of melanin in the irises and how the light scatters off the eyes produces the green eye color. The optical effect of light scattering off the melanin is a distinct way that makes a few eyes green.

Does Eye Color Impact Vision?

Eye color on its own doesn’t impact vision. Melanin concentration in the irises dictates eye color. Typically, it is a cosmetic trait. Moreover, this pigment protects the eyes from excessive sunlight and harmful UV rays.

Updated on March 18, 2024
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6 sources cited
Updated on March 18, 2024
  1. What colour are your eyes? Teaching the genetics of eye colour & colour vision.” Edridge Green Lecture RCOphth Annual Congress Glasgow.

  2. HERC2 (rs12913832) and OCA2 (rs1800407) Genes Polymorphisms in Relation to Iris Color Variation in Belarusian Population.” Science Direct.

  3. Are Blue Eyes in Humans a Mutation?” Institute for Creation Research.

  4. The World’s Popular by Eye Color.” World Atlas.

  5. Why Are My Eyes Changing Color?” American Academy of Ophthalmology.

  6. Eye Color: Unique as a Fingerprint.” American Academy of Ophthalmology.

Will Hunter
Will Hunter
Content Contributor
Will is a content writer for KnowYourDNA. He received his B.A. in Psychology from the University of California, Los Angeles. Will has 7 years of experience writing health-related content, with an emphasis on nutrition, alternative medicine, and longevity.