There are some alleles which are not only expressed when they are in homozygous condition, but also expressed when they are in heterozygous condition. Such alleles are called dominant alleles. The trait represented by such alleles is a dominant trait, or a dominant character, which will be most profusely observed in a population. Example, black/ dark brown color of eye ball is a dominant character mostly seen in people.

On the other hand, there are alleles which gets expressed only when in homozygous condition. Such alleles exhibit recessive traits or recessive characters, which are not commonly found in a population. Example, eye ball colors like green, grey, blue etc. represent recessive character and you will not find many people carrying them.