It has to do with a single gene! More than a decade ago, researchers discovered that one gene (MC1R) on chromosome 16 plays an important role in giving people red hair. MC1R task is to make the protein melanocortin 1. This protein plays an important role in converting red pigment into black pigment. If you end up with only one mutated MC1R gene, red hair can appear in unwanted places, like your beard. When someone inherits two mutated versions of the MC1R-gene (one from each parent), less red pigment is converted into black pigment.
