Expert: Dana Krempels, Ph.D. - 7/6/2007

Question
I'd appreciate a little info about the red hair gene. I have blonde hair as does my baby's father, but our child was born with red hair. Please explain how this happens. Is the red hair inherited from the mother or father, or both.  Thanks!

Answer
Dear Betty,

Hair color in humans is controlled by several different genes, including genes that code for the particular color of pigment (eumelanin is brown; phaeomelanin is red) as well as others that code for how much pigment is deposited in the hair shaft.

In mammals, a protein known as the melanocortin-1 receptor (Mc1r) is one of the key factors in regulating hair and skin color.  The protein is involved in melanogenesis:  the production of melanins.  In most mammals, the protein promotes the formation of black/brown eumelanin.  (We'll call this version of the gene "R").  But certain mutant forms of this same gene cause the production of reddish phaeomelanin.  (We'll call this mutant version "r".)

Rewind to a bit of basic genetics:  Everyone has two copies of every gene, one from mom and one from dad.  So in terms of the melanocortin gene, a person can have two copies of R, two copies of r, or one of each:  s/he can have a "genotype" of RR, Rr or rr.

The brown pigment form of the gene is dominant to the recessive red version.  This means that the R version *masks* the expression of the r version.  So a person with either genotype RR or Rr will have the brown pigment.  A person will have red hair only if his/her genotype is rr, lacking the R version to mask the r version.

Both you and your husband produce eumelanin (brown) in low concentration (which is why your hair is blonde, not brown; other genes control *how much* melanin is deposited in the hair shaft), but your genotypes MUST both be Rr if you produced an rr child.  Your child got one copy of "r" from each of you.

Wow!  That's probably more information than you wanted.  But I hope it helps.

Dana