Why do some dominant traits have two different types of alleles?

you inherit 2 alleles for each genes. one comes from your biological mom and the other comes from you biological father. if the alleles are identical like when both your parents have brown eyes and that it will cause you to have brown eye color. some alleles are dominant while the rest are recessive. the dominant trait is more stronger than recessive trait. It is a strictly relative effect between two alleles of a given gene of any function; one allele can be dominant over a second allele of the same gene, recessive to a third and co-dominant with a fourth. Additionally, one allele may be dominant for one trait but not others.

Explanation:

enzyme active site and substrate specificity

enzymes bind with chemical reactants called substrates. there may be one or more substrates for each type of enzyme, depending on the particular chemical reaction. in some reactions, a single-reactant substrate is broken down into multiple products