Is Eye Color Genetic?

Is Eye Color Genetic? | What Your Eye Color Has to Do With Your History

Eye colors are passed down through generations, but sometimes genetic variations can lead to surprising results in eye colors. Learn about the genetics of eye color in this guide.

Whether eyes are blue or brown, eye color is determined by genetic traits handed down to children from their parents. A parent’s genetic makeup determines the amount of pigment, or melanin, in the iris of the his or her child’s eye. With high levels of brown melanin, the eyes look brown. With minimal levels of the same brown melanin, the eyes look blue. However, a genetic variation can cause a child’s eye color to be unpredictable, resulting in two blue-eyed parents having a brown-eyed child.

Know Your Health: Genetics of Eye Color

Eye colors have evolved over time and have roots in our ancestry. Although eye color is determined by genetic makeup, variations can cause different shades to appear. Learn more about the genetics of eye color, including:

How Is Eye Color Determined?

Genetic makeup determines the amount of melanin in the eye. In eye color, there isn’t blue or green pigment. All eye colors have the same brown melanin incapable of refracting light. The difference in eye colors is due to the concentration and location of the brown melanin on the two layers of the iris. People with brown eyes have melanin on the back layer of the iris and some on the front layer, which absorbs more light and causes the iris to look brown. Eyes with no melanin on the front layer of the iris scatter light so that more blue light reflects out, so that the eyes appear blue.

The chromosomes a child inherits carry genetic information that determines eye color. Differences in the copies received from each parent causes variations in the amount of melanin produced. A region on chromosome 15 has a big part in determining eye color. The OCA2 and HERC2 genes are located in this region.

The OCA2 gene (formerly called the P gene) provides instructions for producing the P protein located in the melanocytes (specialized cells that produce melanin). If more protein is produced, then the eyes received more melanin, and eye color leans toward the brown end of the color spectrum. When less protein is produced, the eyes receive less melanin and eye color leans toward the blue end of the spectrum. Although nearly 75 percent of eye color is controlled by the OCA2 gene, other genes provide a pathway for melanin. These genes can raise or lower melanin levels, causing a child to have more or less melanin than either parent. These variations can result in blue-eyed parents having a brown-eyed child, or brown-eyed parents having a blue-eyed child. The former is more likely than the latter.

Is Eye Color Genetic?

Each cell in the human body normally contains 23 pairs of chromosomes. Chromosome 15 likely contains 600 to 700 genes integral to producing proteins. Two of these genes, OCA2 and HERC2, play a significant role in eye color selection.

Although the OCA2 gene produces the protein responsible for melanin, the HERC2 gene controls the OCA2 gene by turning its protein production on and off. The presence of at least one genetic variation in the HERC2 gene can reduce the amount of melanin produced, leading to lighter eyes. Other genes working with OCA2 and HERC2 have a smaller role, but on rare occasions override OCA2 to determine eye color.

Is Eye Color Inherited?

Eye color was once thought to be the result of a single hereditary trait. It was thought that each person received one eye color gene from each parent, and the dominant gene determined eye color. In this model, the brown-eye color gene was always dominant over the blue-eye color gene, and only two blue-eye color genes could color eyes blue.

Charles and Gertrude Davenport developed the dominant brown eye model in 1907. They suggested that blue eyes were caused by a single recessive gene, and blue-eyed parents could never produce a brown-eyed child. Dominant and recessive genes refer to inheritance patterns, and describe how likely it is for a certain trait to pass from parent to offspring.

Today, we know this model is simplistic, and that many genes determine that eye color. Although we can predict the color of a child’s eyes based on the parent’s eye colors, other genetic factors may alter the outcome.

Can Eye Color Be Predicted?

While it is possible to predict the probability of eye color, genetic factors may alter the outcome. Movie star Elizabeth Taylor’s parents probably did not predict their daughter’s rare violet eyes. Taylor’s eye color is thought to be the result of a genetic mutation in the FOXC2 gene, which causes a specific amount of melanin that produced a striking eye color and may cause double eye lashes as well as heart problems.

With eye color controlled by more than one gene, it is possible for a newborn to inherit any eye color. Predicting eye color is further complicated because it sometimes changes after birth. A baby’s blue eyes can turn brown as more melanin is deposited into the iris over the first three years of life.

What Does Your Eye Color Mean?

According to one theory, almost everyone (99.5 percent) with blue eyes might be able to trace their ancestry back to the same blue-eyed ancestor that lived in the northwest part of the Black Sea region some 6,000 to 10,000 years ago. This is based on the DNA analysis of about 800 blue-eyed people, in which only one person did not have the same blue-eye genetic mutation as the rest of the group. This mutation seems to have occurred during the Neolithic period (or New Stone Age) during the great agricultural migration to the northern part of Europe. Nearly all blue-eyed humans have this same mutation in the same location in their DNA. By contrast, brown-eyed humans have more variation in their DNA when it comes to eye color.

Brown Eyes

The majority of people in the world have brown eyes. The color brown is a result of a high concentration of melanin in the iris causing more light to be absorbed and less light to be reflected. Because of this, brown eyes are more naturally protected from the sun. This likely had evolutionary benefits similar to darker skin being able to withstand the hot sun longer. The genes responsible for skin color are closely linked to those that cause eye color.

Though brown eyes are the most common genetic eye color, there is more genetic variation among those with brown eyes than those with blue eyes. This may account for the variations of brown eye colors. These variations come from different genes on different chromosomes that carry genetic eye color information from our ancestors.

Blue Eyes

Originally, all humans had brown eyes. Some 6,000 to 10,000 years ago, a genetic mutation affecting one gene turned off the ability to produce enough melanin to color eyes brown causing blue eyes. This mutation arose in the OCA2 gene, the main gene responsible for determining eye color. Since blue eyes have survived throughout many generations, researchers think there may have been some evolutionary benefit, though the exact reason is unknown.

Blue eyes are the result of low concentrations of brown melanin, not blue pigmentation. Less melanin allows more light to reflect back to wavelengths on the blue color spectrum, which in turn make eyes appear blue. The reason why eyes are blue is the same reason the sky is blue. Some 8 to 10 percent of humans worldwide have blue eyes.

Green Eyes

Only about 2 percent of the world’s population has green eyes. Green eyes are a genetic mutation that produces low levels of melanin, but more than blue eyes. As in blue eyes, there is no green pigment. Instead, because of the lack of melanin in the iris, more light scatters out, which make the eyes appear green. Changes in light make lighter eyes look like they are changing colors like a chameleon.

Hazel Eyes

Hazel eyes are sometimes mistaken for green or brown eyes. They are not as rare as green eyes, but are rarer than blue eyes. Only about 5 percent of the population worldwide has the hazel eye genetic mutation. After brown eyes, they have the most melanin. . The combination of having less melanin (as with green eyes) and a lot of melanin (like brown eyes) make this eye color unique.

The color combinations in shades of green, brown, and gold are endless with hazel eyes, depending on the concentration of melanin. The light scatters as it does with blue and green eyes.  As with blue and green eyes, hazel eyes may appear to shift colors depending on the light. The eye color doesn’t actually shift, perception does. It is unknown if hazel eyes developed from brown eyes or green.

How does your eye health impact your life?

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The History of DNA

The History of DNA

By Contributing LunaDNA Writer. Last edited by LunaPBC on September 2019

The human hereditary material known as deoxyribonucleic acid, or DNA, is a long molecule containing the information organisms need to both develop and reproduce. DNA is found in every cell in the body, and is passed down from parent to child.

Although the discovery of DNA occurred in 1869 by Swiss-born biochemist Fredrich Miescher, it took more than 80 years for its importance to be fully realized. And even today, more than 150 years after it was first discovered, exciting research and technology continue to offer more insight and a better answer to the question: why is DNA important?  Learn more here about DNA, including:

What is DNA?

DNA is self-replicating material that’s in every living organism. In simplest terms, it is a carrier of all genetic information. It contains the instructions needed for organisms to develop, grow, survive, and reproduce. It’s one long molecule that contains our genetic “code,” or recipe. This recipe is the starting point for our development, but DNA’s interaction with outside influences such as our lifestyle, environment, and nutrition ultimately form the human being.

While most DNA is found in the nucleus of a cell, a small amount can also be found in the mitochondria, which generates energy so cells can function properly. Perhaps the most fascinating part of the process is the fact that nearly every cell in your body has the same DNA.

What is DNA Made of?

DNA is made up of molecules known as nucleotides. Each nucleotide contains a sugar and phosphate group as well as nitrogen bases. These nitrogen bases are further broken down into four types, including:

  • Adenine (A)
  • Cytosine (C)
  • Guanine (G)
  • Thymine (T)

DNA’s structure is a double-stranded helix, and it resembles the look of a twisted ladder. The sugar and phosphates are nucleotide strands that form the long sides. The nitrogen bases are the rungs. Every rung is actually two types of nitrogen bases that pair together to form a complete rung and hold the long strands of nucleotides together. Remember, there are four types of nitrogen bases, and they pair together specifically – adenine pairs with thymine, and guanine with cytosine.

Human DNA is unique in that it is made up of nearly 3 billion base pairs, and about 99 percent of them are the same in every human. However, it’s the sequence of these bases that determines what information is available to both build and maintain any organism.

Think of DNA like individual letters of the alphabet — letters combine with one another in a specific order and form to make up words, sentences, and stories. The same idea is true for DNA — how the nitrogen bases are ordered in DNA sequences forms the genes, which tell your cells how to make proteins. Ribonucleic acid (RNA), another type of nucleic acid, is formed during the process of transcription (when DNA is replicated). RNA’s function is to translate genetic information from DNA to proteins as it is read by a ribosome.

How Does DNA Work?

DNA is essentially a recipe for any living organism. It contains vital information that’s passed down from one generation to the next. DNA molecules within the nucleus of a cell wind tightly to form chromosomes, which help keep DNA secure and in place and store important information in the form of genes to determine an organism’s genetic information.

DNA works by copying itself into that single-stranded molecule called RNA. If DNA is the blueprint, you can think of RNA as the translator of instructions written in the blueprint.  During this process, DNA unwinds itself so it can be replicated. RNA is similar to DNA, but it does contain some significant molecular differences that set it apart. RNA acts as a messenger, carrying vital genetic information in a cell from DNA through ribosomes to create proteins, which then form all living things.

How Was DNA Discovered?

DNA was discovered in 1869 by Swiss researcher Friedrich Miescher, who was originally trying to study the composition of lymphoid cells (white blood cells). Instead, he isolated a new molecule he called nuclein (DNA with associated proteins) from a cell nucleus. While Miescher was the first to define DNA as a distinct molecule, several other researchers and scientists have contributed to our relative understanding of DNA as we know it today. And it wasn’t until the early 1940s that DNA’s role in genetic inheritance was even begun to be researched and understood.

Who Discovered DNA?

The full answer to the question who discovered DNA is complex, because in truth, many people have contributed to what we know about it. DNA was first discovered by Friedrich Miescher, but researchers and scientists continue to expound on his work to this day, as we are still learning more about its mysteries. As it turned out, Miescher’s discovery was just the beginning.

Credit for who first identified DNA is often mistakenly given to James Watson and Francis Crick, who actually just furthered Miescher’s discovery with their own groundbreaking research nearly 100 years later. Watson and Crick contributed largely to our understanding of DNA in terms of genetic inheritance, but much like Miescher, long before their work, others also made great advancements in and contributions to the field.

  • 1866 — Before the many significant discoveries and findings, Gregor Mendel, who is known as the “Father of Genetics,” was actually the first to suggest that characteristics are passed down from generation to generation. Mendel coined the terms we all know today as recessive and dominant.
  • 1869 — Friedrich Miescher identified the “nuclein” by isolating a molecule from a cell nucleus that would later become known as DNA.
  • 1881 — Nobel Prize winner and German biochemist Albrecht Kossel, who is credited with naming DNA, identified nuclein as a nucleic acid. He also isolated those five nitrogen bases that are now considered to be the basic building blocks of DNA and RNA: adenine (A), cytosine (C), guanine (G), and thymine (T) (which is replaced by uracil (U) in RNA).
  • 1882 — Shortly after Kossel’s findings, Walther Flemming devoted research and time to cytology, which is the study of chromosomes. He discovered mitosis in 1882 when he was the first biologist to execute a wholly systematic study of the division of chromosomes. His observations that chromosomes double is significant to the later-discovered theory of inheritance.
  • Early 1900s — Theodor Boveri and Walter Sutton were independently working on what’s now known as the Boveri-Sutton chromosome theory, or the chromosomal theory of inheritance. Their findings are fundamental in our understanding of how chromosomes carry genetic material and pass it down from one generation to the next.
  • 1902 — Mendel’s theories were finally associated with a human disease by Sir Archibald Edward Garrod, who published the first findings from a study on recessive inheritance in human beings in 1902. Garrod opened the door for our understanding of genetic disorders resulting from errors in chemical pathways in the body.
  • 1944 — Oswald Avery first outlined DNA as the transforming principle, which essentially means that it’s DNA, not proteins, that transform cell properties .
  • 1944-1950 — Erwin Chargaff discovered that DNA is responsible for heredity and that it varies between species. His discoveries, known as Chargaff’s Rules, proved that guanine and cytosine units, as well as adenine and thymine units, were the same in double-stranded DNA, and he also discovered that DNA varies among species.
  • Late 1940s — Barbara McClintock discovered the mobility of genes, ultimately challenging virtually everything that was once thought to be. Her discovery of the “jumping gene,” or the idea that genes can move on a chromosome, earned her the Nobel Prize in Physiology.
  • 1951 — Roslind Franklin’s work in X-ray crystallography began when she started taking X-ray diffraction photographs of DNA. Her images showed the helical form, which was confirmed by Watson and Crick nearly two years later. Her findings were only acknowledged posthumously.
  • 1953 — Watson and Crick published on DNA’s double helix structure that twists to form the ladder-like structure we think of when we picture DNA.

When Was DNA Discovered?

What we know about DNA today can be largely credited to James Watson and Francis Crick, who discovered the structure of DNA in 1953. Despite there being many important and contributing discoveries both before and after their work, this is the year they discovered DNA’s double helix, or spiraling, intertwined structure, which is fundamental to our current understanding of DNA as a whole.

The Future of DNA

The future of DNA has great potential. As researchers and scientists continue to advance what we know about the complexities of DNA and the insights it codes for, we can imagine a world with less and better-managed disease, longer life spans, and a personalized view of medicine that’s specifically applicable to individuals rather than the population as a whole.

DNA insights are already enabling the diagnosis and treatment of genetic diseases. Science is also hopeful that medicine will advance to be able to leverage the power of our own cells to fight disease.  For example, gene therapy is designed to introduce genetic material into cells to compensate for abnormal genes or to make a therapeutically beneficial protein.

Researchers also continue to use DNA sequencing technology to learn more about everything from combating infectious disease outbreaks to improving nutritional security.

Ultimately, DNA research will accelerate breaking the mold of the one-size-fits-all approach to medicine. Every new discovery in our understanding of DNA lends to further advancement in the idea of precision medicine, a relatively new way doctors are approaching healthcare through the use of genetic and molecular information to guide their approach to medicine. With precision or personalized medicine, interventions take into consideration the unique biology of the patient and are tailored individually to each patient, rather than being based on the predicted response for all patients. Using genetics and a holistic view of individual genetics, lifestyle, and environment on a case-by-case basis, doctors are better able to not only predict accurate prevention strategies, but also suggest more effective treatment options.

We’ve come leaps and bounds from where we were in terms of our understanding of DNA 150 years ago. But still, there is much to learn. And with the potential that a deeper understanding of DNA will improve human health and quality of life across our world, no doubt, the research will continue. A full understanding of DNA of and between all living things could one day contribute to solving problems like world hunger, disease prevention, and fighting climate change. The potential truly is unlimited, and to say the least, extremely exciting.

How To Do More With Your DNA

Until recently, individuals were sources of samples in the traditional research model. Today, the gap between research and individual is closing and the community is coming together to contribute health data to support research at scale, advance science, and accelerate medical discoveries at LunaDNATM.

There are so many treatments and cures to diseases that are close to being discovered, and your unique DNA data can help revolutionize the future of medicine.

Luna is bringing together individuals, communities, and researchers to better understand life. Directly drive health discovery by joining the Tell Us About You study. The more we come together to contribute health data for the greater good, the quicker and more efficient research will scale, and improve the quality of life for us all.  

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Evolution Hypothesis

Outpaced Evolution: A New Hypothesis

For thousands of years, humans have evolved to survive and thrive in environments fraught with a multitude of different challenges, creating an environment of continuous stress.

From the hunting and gathering struggle for food on a daily basis, to a constant vigil required to protect ourselves from predators, such stressors have enabled humans to become skilled in survival and prepared to address challenges.

In the developed world today, however, food is no longer scarce and predators no longer require us to be alert and ready for flight or fight. We have broken free of the majority of these natural challenges in what is the blink of an eye on the evolutionary timescale. Consequently, the evolutionary rate of adoption is not able to keep up with the rapid change of human condition.

A New Hypothesis

I predict that if we don’t implement challenges in our life on a daily basis, and purposefully create healthy stress across all of our systems, then the results for most of us will be negative outcomes to our health and wellbeing in our later years.

What Are We Fighting For?

Muscular strength and physical endurance were once necessary for chasing down prey for food and for defense against physical threats.  We taxed our bodies physically on a daily basis, though it was not called exercise. Today, lack of physical activity over our adult lives severely impacts our muscle health, flexibility, bone density, balance, and joint/ligament health. In combination with an abundance of high calorie foods, it also can lead to diabetes, obesity, and other chronic problems.

Our ancestors did not have the time or luxury to worry about or contemplate meaning and purpose in life. Every morning they arose to address the multitude of challenges thrown at them, in their efforts to survive. We no longer need to rise each morning and fight for survival, removing what was a key reason for being, our “raison d’etre”.

Can we survive today in a state where nothing drives us, inspires us, or challenges us?”

In the long term it’s impossible to emotionally thrive in this spiritual and intellectual vacuum unless we find our own raisons d’etre. At some point one might lose the desire to get up in the morning and face the day.

Microbiome Evolution

Not surprisingly, even our microbiomes evolved in support of our survival, in what were more challenging times. We developed a symbiotic balance with many important microbes within our microbiome communities. The balance may be at risk for many of us depending on our nutritional choices. For example, food once came from natural sources and we had daily exposure to a rich environment of diverse microbes. This provided access to a rich set of microbes to colonize different areas of our body. Healthy microbes helped us break down hard to digest foods such as fiber from plants and raw meat. These microbes became valuable partners in maintaining digestive and physical health. Some provided a first defense against disease and pathogens.

Today, we have the choice of eating processed foods that may contain no microbes, and that are simple to digest, such as simple sugar, processed grains, and processed meats. The lack of microbes impacts the diversity of our gut microbiome and possibly, more impactfully, may no longer be providing fuel for the the healthy fiber digesting microbes that also have antibiotic resistant properties.

Depleting these microbes leaves space for other microbes to colonize our gut. Microbes that thrive on processed food and sugar, microbes that may not be healthy or even pathogenic, impacting our microbiome balance. This imbalance may contribute to disorders such as leaky gut, SIBO, Crohn’s and Colitis, and simple food allergies.

The Gut Brain Connection

New research points to the effect of our microbiome on mental health, due to the gut brain connection, and effectiveness of cancer immunotherapy treatments. The science in this area is new. Due in large part to the low cost of acquiring genomic data, it is now possible to fund large scale discovery studies on the link between our health and our microbiome. Over time, the links between our microbiome and our health will become much clearer, as will the actions we can take. For now, it is clear that a link exists.

We are fortunate to live in a world where historic challenges no longer plague us. As change is outpacing evolution, it is incumbent on us to modify our lifestyle in order to thrive in this new world. Don’t shy away from challenges in life… embrace them. Don’t be tempted to always take the easy path whether it be sitting all day, eating fast food, or avoiding difficult intellectual and emotional situations. Lead a balanced life of activity, continuous learning, leisure time, and time with family and friends. Eat a balanced meal of fruits, vegetables, and unprocessed foods. And don’t shy away from life’s challenges, for they’re there to help us live long and prosper.

Bob Kain is the chief executive officer at LunaPBC™, a public benefit corporation that manages LunaDNA™, the first community-owned health and DNA data platform dedicated to advancing health research and accelerating medical breakthroughs. Learn more about the team at Luna by visiting our team page here.