In human genetics, hazel eyes are a recessive characteristic. Lighter eye colors are recessive to darker eye colors; this means that brown eyes are dominant over every other eye color.
All humans inherits from their parents two alleles, or forms of genes, that govern eye color. The HERC2 gene has two alleles, brown and blue. The other genes for eye color, the gey and bey2 genes, work together to dictate the different shades. Each person's eye color depends on which two alleles they inherit.
The brown HERC2 allele is dominant overall, so anyone that inherits a brown HERC2 allele will have brown eyes, no matter what the other allele is. The combination of bey2 and gey make brown, green, hazel or blue eyes. These different alleles dictate how much melanin to make, and more melanin means darker eye color.