I was at KFC last night, and there was an African-American family at the table next to me. The mother, father, and 9-ish year old sister were all pretty light skinned, and the son, probably around 4 or 5, was very dark skinned. My question is; is skin tone a recessive gene that both parents could have carried and given to this child? What’s the deal?
There is not a single gene that controls skin color. Skin pigmentation is known as polygenic. So it is possible to get all sorts of skin colors. The genes are also all incompletely dominant. This mean that if A = dark pigmentation and a = light pigmentation, then AA is darker than Aa which is darker than aa.
So let’s look at your example. For simplicity’s sake let’s say that skin color is polygenic across 3 loci: A, B, and C.
Mother’s genotype = AaBbCc (in the middle of the color range)
Father’s genotype = AaBbCc (same genotype as mother’s)
They have a 1 in 64 chance of producing a child who is AABBCC with the pigment gene at all loci.
I should say that AABBCC is homozygous for the pigment gene at all loci.