As we very clearly understand, the offspring inherit the characteristics of their parents by passing genes. Gregor Mendel was the first researcher to establish this fact. He suggested that every species contains two copies of every gene inherited from each parent in sexual reproduction. If the two copies are same then it is termed as homozygous otherwise heterozygous. In a heterozygous organism having two dissimilar genes or alleles one gene is dominant over another and dictates the phenotype of the organism. Sometimes incomplete dominance is also observed in some cases. This phenomenon was termed as Mendel's law by him.