Genetic mutation makes those brown eyes blue (2024)
People with blue eyes have a single, common ancestor, according to new research.
A team of scientists has tracked down a genetic mutation that leads to blue eyes. The mutation occurred between 6,000 and 10,000 years ago, so before then, there were no blue eyes.
"Originally, we all had brown eyes," said Hans Eiberg from the Department of Cellular and Molecular Medicine at the University of Copenhagen.
The mutation affected the so-called OCA2 gene, which is involved in the production of melanin, the pigment that gives color to our hair, eyes and skin.
"A genetic mutation affecting the OCA2 gene in our chromosomes resulted in the creation of a 'switch,' which literally 'turned off' the ability to produce brown eyes," Eiberg said.
The genetic switch is located in the gene adjacent to OCA2 and rather than completely turning off the gene, the switch limits its action, which reduces the production of melanin in the iris. In effect, the turned-down switch diluted brown eyes to blue.
If the OCA2 gene had been completely shut down, our hair, eyes and skin would be melanin-less, a condition known as albinism.
"It's exactly what I sort of expected to see from what we know about selection around this area," said John Hawks of the University of Wisconsin-Madison, referring to the study results regarding the OCA2 gene. Hawks was not involved in the current study.
Baby bluesEiberg and his team examined DNA from mitochondria, the cells' energy-making structures, of blue-eyed individuals in countries including Jordan, Denmark and Turkey. This genetic material comes from females, so it can trace maternal lineages.
They specifically looked at sequences of DNA on the OCA2 gene and the genetic mutation associated with turning down melanin production.
Over the course of several generations, segments of ancestral DNA get shuffled so that individuals have varying sequences. Some of these segments, however, that haven't been reshuffled are called haplotypes. If a group of individuals shares long haplotypes, that means the sequence arose relatively recently in our human ancestors. The DNA sequence didn't have enough time to get mixed up.
"What they were able to show is that the people who have blue eyes in Denmark, as far as Jordan, these people all have this same haplotype, they all have exactly the same gene changes that are all linked to this one mutation that makes eyes blue," Hawks said in a telephone interview.
Melanin switch The mutation is what regulates the OCA2 switch for melanin production. And depending on the amount of melanin in the iris, a person can end up with eye color ranging from brown to green. Brown-eyed individuals have considerable individual variation in the area of their DNA that controls melanin production. But they found that blue-eyed individuals only have a small degree of variation in the amount of melanin in their eyes.
"Out of 800 persons we have only found one person which didn't fit — but his eye color was blue with a single brown spot," Eiberg told LiveScience, referring to the finding that blue-eyed individuals all had the same sequence of DNA linked with melanin production.
"From this we can conclude that all blue-eyed individuals are linked to the same ancestor," Eiberg said. "They have all inherited the same switch at exactly the same spot in their DNA." Eiberg and his colleagues detailed their study in the Jan. 3 online edition of the journal Human Genetics.
That genetic switch somehow spread throughout Europe and now other parts of the world.
"The question really is, 'Why did we go from having nobody on Earth with blue eyes 10,000 years ago to having 20 or 40 percent of Europeans having blue eyes now?" Hawks said. "This gene does something good for people. It makes them have more kids."
Jeanna Bryner
The study you mentioned about the origins of blue eyes ties into genetics, mutations, and the inheritance of traits. The research focused on a specific genetic mutation that affects the OCA2 gene, influencing melanin production in the iris and resulting in the emergence of blue eyes. This mutation, traced back to around 6,000 to 10,000 years ago, essentially acted as a switch that limited the production of melanin, diluting brown eyes to blue.
Hans Eiberg and his team at the University of Copenhagen delved into this genetic switch, which resides near the OCA2 gene. Rather than completely shutting down the gene, this switch modulates its action, reducing melanin production in the iris. The study scrutinized DNA sequences of blue-eyed individuals across various regions, analyzing the mitochondrial DNA to trace maternal lineages and identify shared haplotypes, indicating a recent common ancestry among blue-eyed individuals.
Moreover, the research illuminated how this mutation affects the spectrum of eye colors. While brown-eyed individuals exhibit considerable variation in DNA controlling melanin production, blue-eyed individuals showcase minimal variation in this aspect. This uniformity in the genetic sequence linked with melanin production supports the conclusion that all blue-eyed individuals share a common ancestor who inherited the same genetic switch.
The evolution of this genetic trait prompts questions about its spread throughout Europe and other regions over time. Scientists like John Hawks from the University of Wisconsin-Madison speculate on the advantageous nature of this mutation, potentially contributing to higher reproductive success in individuals possessing this gene variant.
This study, documented in the journal Human Genetics, not only sheds light on the genetic underpinnings of eye color but also raises intriguing queries about the rapid emergence and prevalence of blue eyes in human populations over the last several thousand years.
OCA2 provides instructions for making the protein called P protein which is located in melanocytes which are specialized cells that produce melanin, and in the cells of the retinal pigment epithelium. Melanin is responsible for giving color to the skin, hair, and eyes.
gene, they will always have blue eyes, because the HERC2 gene can't make the broken OCA2 gene work. Likewise, if a person has a HERC2 gene which doesn't work, the OCA2 gene will “underachieve,” failing to produce enough pigment to make brown eyes, resulting in blue eyes.
The genetic switch is located in the gene adjacent to OCA2 and rather than completely turning off the gene, the switch limits its action, which reduces the production of melanin in the iris. In effect, the turned-down switch diluted brown eyes to blue.
Blue eyes occur because of low melanin levels in the iris of the eye. In most humans this seems to occur due to a mutation in a gene expression region near the OCA2 gene (locus). The OCA2 gene makes a protein that transports a melanin precursor (tyrosine) across cell membranes.
To date, eight genes have been identified which impact eye color. The OCA2 gene, located on chromosome 15, appears to play a major role in controlling the brown/blue color spectrum. OCA2 produces a protein called P-protein that is involved in the formation and processing of melanin.
A mutant gene that produces brown eyes (bw) is located on chromosome #2 of Drosophilia melangaster, whereas a mutant gene producing bright red eyes, scarlet (st) is located on chromosome #3.
“The changes are always going to go from light to dark, not the reverse,” Jaafar says. “If you have brown early on, they're not going to become blue.” What's more, about 10 percent of babies will continue to experience changes in eye color (albeit subtle) until they're adults.
For most people, eye color will not change significantly past infancy. If you notice a change in your eye color, set an appointment with an eye doctor to help find the cause. If it's a major change that happens suddenly, ask for an urgent appointment.
With this change, gray now tops the list as the rarest eye color. Gray eyes may contain just enough melanin in the front layer to dim the blue wavelengths of light that are reflected back by the tissue of the eye. Dark gray eyes have a bit more melanin in the front layer than pale gray eyes.
Both ocular albinism and oculocutaneous albinism result from mutations in genes involved in the production and storage of melanin. Another condition called heterochromia is characterized by different-colored eyes in the same individual.
Although the deep blue eyes of some people such as Elizabeth Taylor can appear purple or violet at certain times, "true" violet-colored eyes occur only due to albinism. Eyes that appear red or violet under certain conditions due to albinism are less than 1 percent of the world's population.
Can a child inherit two different eye colors from the mother and father? Technically, yes. They will inherit several genes, but it's a complete toss up how many they will get from each parent.
Hazel eyes are generally a combination of brown, green, and gold. Sometimes, blue or even amber can make an appearance in hazel eyes, too. Often, hazel-colored eyes have a different hue around the pupil than on the eye's outer rim.
Scientists have already identified over 100 different genes that influence hair, skin and eye pigmentation but here we are going to keep it simple and only work with BROWN and BLUE eye colour. In general, the allele for brown eyes is DOMINANT over the allele for blue eyes (which is then called the RECESSIVE allele).
Just a little more melanin, and their eye color may be green or hazel. Brown eyes, which are the most common, are the result of very active melanocytes secreting lots of melanin. Brown eyes are likely to remain brown throughout life.
Your MSM, color changing, and eye lightening eye drop products are not generally recognized as safe and effective (GRASE) for their above-referenced uses and, therefore, these products are “new drugs” under section 201(p) of the FD&C Act, 21 U.S.C. 321(p).
In as much as 15 percent of the white population (or people who tend to have lighter eye colors), eye color changes with age. People who had deep brown eyes during their youth and adulthood may experience a lightening of their eye pigment as they enter middle age, giving them hazel eyes.
What's the rarest eye color? Not counting colors like red/pink from conditions like albinism, the rarest of the main eye colors is green. About 2% of people worldwide have green eyes.
With aging or high blood lipid levels its clarity may change causing a cloudy appearance that the patient or observer may call "gray." Hence a brown or blue eye may turn gray. A scarred or swollen cornea also has a gray appearance. The color of the iris behind an abnormal cornea is not changed.
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