Melanin also serves as a level of protection from the sun. For example, brown eyes have lots of melanin in the iris, while blue and green eyes have less melanin. The more melanin you have, the darker your skin will be. However, one thing that is for sure is that the color of your eyes has everything to do with melanin. It turns out that eye color and all of its variations are more complicated than that. Now, as scientists have learned more about the complexity of genes and gene mutations, we know that predicting eye color based on Mendel’s punnet square theory isn’t the whole story. That theory persisted for hundreds of years. If a person with Bb brown eyes has a child with someone else who has a Bb mix or a child with a blue-eyed partner (bb), they have a chance of having a child with lighter eye colors. However, some people with brown eyes have one dominant gene (B) and one recessive blue-eyed gene (b), which means they contribute (Bb) to the mix – (Brown-blue). If you inherited both “big Bs” (brown-brown), your children will only have brown eyes (BB). The general theory around the idea of inherited eye color goes like this: Eye color is one of the easiest things to pop into a punnet square because brown eyes are dominant. If you remember your first lessons in genetics at the middle school or high school levels, odds are you remember studying Gregor Mendel and his punnet squares. However, the color of your irises can make a bit of a difference in how you view the world. However, for the most part, your eye color doesn’t put you at risk for vision conditions (an exception being albinism ). And so are many of the most common eye conditions and eye diseases leading to vision loss. It makes them have more kids.Your eye color is 100% linked to specific genes. "This gene does something good for people. "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. That genetic switch somehow spread throughout Europe and now other parts of the world. 3 online edition of the journal Human Genetics. "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. "From this we can conclude that all blue-eyed individuals are linked to the same ancestor," Eiberg said. "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. But they found that blue-eyed individuals only have a small degree of variation in the amount of melanin in their eyes. Brown-eyed individuals have considerable individual variation in the area of their DNA that controls 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. The mutation is what regulates the OCA2 switch for melanin production. "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. The DNA sequence didn't have enough time to get mixed up. If a group of individuals shares long haplotypes, that means the sequence arose relatively recently in our human ancestors. Some of these segments, however, that haven't been reshuffled are called haplotypes. Over the course of several generations, segments of ancestral DNA get shuffled so that individuals have varying sequences. They specifically looked at sequences of DNA on the OCA2 gene and the genetic mutation associated with turning down melanin production. This genetic material comes from females, so it can trace maternal lineages. Hawks was not involved in the current study.Įiberg and his team examined DNA from mitochondria, the cells' energy-making structures, of blue-eyed individuals in countries including Jordan, Denmark and Turkey. "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. If the OCA2 gene had been completely shut down, our hair, eyes and skin would be melanin-less, a condition known as albinism. In effect, the turned-down switch diluted brown eyes to blue. 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.
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