People often assume that a person who has red hair must have Irish heritage. Sometimes, that might be correct. However, it is entirely possible for a person to have red hair and absolutely no Irish ancestors. The reason has to do with the genetics that influence red hair.
It is understandable that people associate red hair with Irish ancestry. Over 10 percent of 23andMe customers of Irish heritage, who have four grandparents who were born in Ireland, have red hair. In other words, there are situations where having red hair is an indicator of Irish heritage. That doesn’t mean that everyone who has red hair is Irish, though.
Hair color is determined by the amount of eumelanin that is in a person’s hair. Those that have only a little eumelanin have blond hair. Those with a moderate amount of it have brown hair, and those who have a lot of it have black hair.
Red hair is connected to pheomelanin. The more pheomelanin that a person has in his or her hair, the redder it looks. People who have auburn or strawberry blond hair have some pheomelanin and some eumelanin.
There is a gene that is associated with red hair that is called MC1R. This gene converts pheomelanin into eumelanin. In other words, this gene takes the type of melanin that makes red hair and converts it into the type of melanin that can make blond, brown, or black hair (depending on the amount of it). The result is that naturally red hair is rather rare.
It is possible for the MC1R gene to have a mutation. This mutation prevents the gene from being able to turn pheomelanin into eumelanin. The mutated version of MC1R is recessive to the regular MC1R gene (which is dominant). This means that a person will not end up with red hair unless they happen to receive two mutated MC1R genes.
Another possibility is for a person to receive one regular MC1R gene, and one mutated MC1R gene, from his or her parents. That’s not enough for the person to end up with red hair. Instead, this person will have blond, or brown, or black hair. The person also might, or might not, have freckles.
In other words, the people who end up with one functioning MC1R gene, and one mutated MC1R gene, are “carriers”. They don’t end up with red hair, but are able to pass on the gene that causes red hair to their offspring. If their partner also has a mutated MC1R gene, it is possible for one of their children to inherit red hair. That can happen even if neither of the parents have red hair themselves.
Image by mendhak on Flickr.
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