Humans only have a few eye colors and only four ABO-based blood types. How can DNA tests definitively identify individuals when many people have brown eyes or type A blood?

The correct answer is that variable number repeats are used in DNA tests; they have hundreds of possible lengths. Eye color is determined by variations in a person's genes. Most of the genes associated with eye color are involved in the production, transport, or storage of a pigment called, melanin. Eye color is directly related to the amount and quality of melanin in the front layers of the iris.