Characteristics or traits are genetic entities whose expression depends upon several factors, including mode of inheritance or how that trait is passed on. One can refer to dominant, recessive or co-dominant traits.

A dominant trait requires that only one gene at a particular locus be present in order for that trait to be expressed phenotypically. A recessive trait requires that both genes be the same in order for that phenotype to appear. A good illustration of this is human eye-color. In humans, brown eyes are dominant to blue-eyes. Because genes code for proteins or pieces of proteins called polypeptides, then it is easy to see why the brown eye pigment would be dominant to the blue eye pigment since it is darker and would hide the lighter color.

A co-dominant trait is one that is somewhere in the middle between the two parental phenotypes...