Which genes underlie red hair, and how can two parents with brown hair have a redheaded and freckled child?

You may have met a redheaded kid, with flaming red hair and freckles on his nose, whose parents have dark or brown hair, without a hint of red. This happens quite often and makes us wonder where this significantly different color came from? Did the child get his red hair from his father, whose grandfather’s uncle was, as told by his family, redheaded? Or maybe from his mother, who has a half-sister with red hair? The answer is almost always: from both.

The main gene that underlies red hair is Melanocortin 1 Receptor, or MC1R. As implied by its name, the protein that it encodes is a receptor that plays a role in pigment synthesis. This gene has several versions (alleles), one of which is related to red hair. Red hair is a recessive trait, which means that only those who get two “redhead” versions of the gene, one from the mother and one from the father, will have red hair. In case one of the parents passed on a version of the gene associated with dark hair, for example, the individual will have dark hair and will simply be a carrier of the “redhead” gene, which he could pass on to his children. This is how a child of two non-redhead parents can grow a red mane, and this is also why red hair must be inherited from both parents and not only from one of them.

While almost all redheads have two copies of the “redhead” version of the MC1R gene, not everyone who has two such copies will necessarily be redheaded. As with most traits, more than one gene determines hair color, and while MC1R is definitely the main player, a few other genes also affect the trait. In a study published in 2018 researchers examined 350 thousand people from the UK and found eight different genes, specific versions of which were associated with red hair, while carriers of other versions of these genes did not have red hair, even if they had two “redheaded” versions of MC1R. Most of the subjects in the study were of European descent and other populations may have different versions of these genes, or other genes that affect hair color, and that we are yet to discover

Few But Not Extinct

Red hair is relatively rare in the general population - according to estimates, only two percent of the global population have red hair, not accounting for those whose hair color originated from a bottle, naturally. In some places, such as Scotland and Ireland, red hair is more common. It is estimated that about ten percent of the population of Ireland is redheaded. 

Redheads are often considered to have special features of character, such as being rebellious, defying authority and conventions and possibly a bit quick to get angry. While scientific studies found no evidence to support these views, some physical traits are indeed characteristic of redheads: they have lower pain tolerance and require larger doses of painkillers, and even anesthetics. Redheads also get colder faster - consider them while arguing about the temperature of the air conditioner in the office.  

Since red hair is a recessive trait, the children of two redheaded parents will almost always be redheaded as well. In contrast, if only one parent is redheaded and the other has brown hair, there is a higher chance that the children will display the dominant trait and will have brown hair. This could be the source of the baseless rumors that redheads are in danger of becoming extinct. Do not worry: redheads are not going anywhere. The children of those “mixed couples”, in which one partner is redheaded and the other is not, will most likely not have red hair - but they will be carriers of the “redhead” gene. They will pass on this gene to some of their children and so forth, until in one of the next generations their descendant will encounter another “redhead” gene, which may result in a redheaded and freckled girl. The grandparents and uncles will be surprised: where did she get that hair? From her mother, as well as from her father.  

Do you have red hair? If so, who among your relatives has red hair like you? Did your parents know that they have this gene, or were they surprised to find out that their child has red hair?