Don't miss Nicole Giladi's beautiful "Little Redheads Across America" photo book.
Book tells why Mom is tickled pink to have a little redhead (USA TODAY, March 10, 2010)
Cardinal Rules (from Boston Globe, March 10, 2010)
The Pain of Being a Redhead (NY Times Aug 6, 2009)
Redheads' Extra Pain May Cause fear of Dentist (CNN July 31, 2009)
Hair color is one of the most variable phenotypes in the human population, and is often associated with individual’s ethnic background and geographical origin. Natural hair color ranges from black, to blonde, to red, and everything in between. Red hair is the rarest color among all, accounting for only 1% of total human population. The majority of redheads are concentrated along the edges of eastern and western Europe, particularly in Scotland and Ireland. It is estimated that around 4% of the European population are red headed, while as much as 13% of the Scottish and 10% of the Irish are red headed. In Ireland, an estimated 40% of the population are red hair carriers. In the United States, 2 percent of individuals have naturally red shades of hair, making US the single country with the largest population of redheads (~6 million).
The Red Hair Gene
Of course there isn't a real red hair gene. There is a gene that comes in many versions (variants), some of which lead to red hair. This gene is called MC1R. Like any other gene, the MC1R gene has the instructions for making a protein. In this case, the MC1R protein. One of the MC1R protein's major jobs is to turn red pigments into brown pigments. Therefore this means that everyone makes red pigments in their hair, and it is the amount of brown pigments that dictates one's hair color. Only people who have versions of MC1R protein that do not make brown pigments builds up the red pigment, and so have red hair.
Since we have two copies for most of our genes--one from mom and one from dad, both copies of your MC1R gene need to be the red hair versions (two r alleles) to become a redhead. People with one red hair copy and one regular copy of the MC1R gene still make enough brown pigment and are normally not redheaded.
The Science of The Red Hair Gene
The MC1R is one of the key protein in regulating pigment production in human hair and skin. It is a member of the G-protein-coupled receptor family, and functions at the surface of special pigment producing cells called melanocytes to regulate pigment production in mammals. Differences in human skin and hair colors are due to variations in the amount of different types of melanin (pigments) and are primarily determined by genetics.
The human MC1R is highly polymorphic, with over 2 dozen SNPs (single nucleotide polymorphism) identified so far, making it one of the most highly variable genes in human. Among the different MC1R variants, several have been shown to have strong associations with red hair and pale skin (and are referred to as the r allele or the red hair allele throughout this website). Most redheaded individuals are either homozygous or compound heterozygous for these variants. Still several other variants were known to have weak associations with the red hair color. Hair color is determined by the amount of two pigments called eumelanin and pheomelanin that are in your hair. The amount of eumelanin in your hair gives you a range from blonde to black—a little eumelanin and you are blonde, an intermediate amount, brown, and a lot, black. Pheomelanin gives red color to the hair. The more pheomelanin in your hair, the redder it is. So hair color is a mixture of how much eumelanin and phomelanin is in your hair. For example, strawberry blonde is a little of each, auburn is some eumelanin and pheomelanin and a redhead is very little eumelanin and lots of pheomelanin.
The amounts of eumelanin and Pheomelanin present in your hair is genetically determined by the action of your MC1R. However, several versions of the MC1R gene either do not convert phomelanin into eumelanin or do so very poorly. A copy of regular MC1R gene keeps most human from being redheads. Current theories on inheritance of hair color besides red, can be found here.
With the increase of migration and inter-ethnic mixing, it is said to become harder for two redheads (or carriers) to form family and have children. As a result, the redhead population will gradually decline over the next 100 years. However, the number of redheads might decline, the frequency of red hair genotypes (recessive r alleles) should remain fairly constant in the population from generation to generation.