Which one of the following genotypes represents a similar skin color?
Answer & explanation
Correct answer: option 1
The correct answer is Option (1) → AABBCc and AaBBCC
Human skin colour is a polygenic trait. Three genes, A, B and C, control it. Each dominant allele (A, B, C) adds the same amount of dark colour, and each recessive allele (a, b, c) adds none. So the number of dominant alleles decides the shade, not which genes they belong to. Count the capital letters in each genotype:
Option (1) AABBCc = 2 + 2 + 1 = 5; AaBBCC = 1 + 2 + 2 = 5. The same number, so the same skin colour.
Option (2) AABBcc = 2 + 2 + 0 = 4; AabBCc (as printed) has three capital letters = 3. Different shades.
Option (3) AaBbcc = 1 + 1 + 0 = 2; aaBBCC = 0 + 2 + 2 = 4. Different shades.
Option (4) aabbcc = 0, the lightest skin; AABBCC = 6, the darkest skin. These are the two extremes.