Differences in skin color are largely due to differences in the amount of melanin, a dark
pigment produced by skin cells.
At least three genes control the synthesis of melanin.
Each gene has two forms: an allele for high melanin production, or dark skin (A,B,C),
and an allele for low melanin production, or light skin (a,b,c). Each dark skin allele
(A,B,C) in the genotype adds a small but equal amount of pigment to the skin. There
are seven different shades of skin color ranging from very dark (AABBCC) to very light
(aabbcc). Most individuals produce a medium amount of melanin and are of
intermediate skin color (AaBbCc).
The following Punnett square shows the possible offspring from a cross between two
individuals of intermediate skin color.
AaBbCc X AaBbCc