Some traits are inextricably tied to your ancestry. Both eye color and hair color are influenced by a lot more than one gene!) (It’s actually more complicated than I’m showing here. DelRossoĪnd the chances of a blue eyed child are even higher if one of the parents has that recessive trait. But if two carriers for blue eyes have a child, they can have a blue eyed child! Image by N. Someone like this is called a carrier, because they invisibly carry the DNA for blue eyes.Ī recessive gene can hide in a family, and take a few generations to reappear. Even though they have the DNA for blue, it’s hidden. So someone with one brown allele and one blue allele would have brown eyes. You won’t see these light colors unless you inherit two copies of the allele. The allele for lighter colors (like blue eyes!) is weaker, or recessive. You only need to inherit one brown eye allele to see the color. So for example, a gene that affects eye color could come in two versions: a blue eye allele, and a brown eye allele.įor most pigmentation genes, the allele for darker colors is stronger, or dominant. Each gene can come in slightly different versions, called alleles. Let’s unpack what it means to be a genetic carrier.Įveryone has two copies of each gene, one from their mom and one from their dad. The most likely genetic explanation for your friend is that her father is a carrier for blue eyes and blonde hair. (Image from Berkeley) Hidden DNA for lighter eyes and hair The odds of a new mutation causing blue eyes is very unlikely, especially if two siblings in the family have blue eyes. 1The chance of this mutation being in a specific spot in that gene is even lower. Based off these estimates, one would expect to find one mutation in a specific gene per one million people. Scientists have studied how good these repair enzymes are, and how often they make mistakes. So even if a mutation occurs, these enzymes swoop in and try to correct them! Usually our cells catch these mistakes and fix them.īut occasionally, some mutations get missed and eventually inherited. Remember, our bodies have “proofreading” repair machinery that fix these mutations.
Over time, this genetic difference spread and became more common.īut the chance of anyone having a new random mutation that does this is pretty low. (Image: Wikimedia) New eye and hair mutationsīlue eyes actually originally came about because of mutations! Thousands of years ago, someone had a random change in the genes that affect eye color. Since poor vision is part of the diagnosis for albinism, if your friend does not have poor vision, they are not albino. People with albinism have severe vision problems, often becoming “legally blind.” Albinism is an inherited genetic condition that results in loss of melanin pigment in the eyes, hair and skin. A new mutation in the eye color and hair genesĪlbinism can be ruled out if your friend is not light-skinned.The father carries some DNA for lighter hair and eyes.There’s a few possible ways in which your friend ended up with blonde hair and blue eyes. Your biology teacher is most certainly right that blonde hair and blue eyes are indeed typically recessive traits! That’s actually the main reason why your friend and his sister could have inherited light eyes and hair, despite one parent having darker eyes/hair.
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