Mendel's law of dominanace means that there will be an allele which will join to form a certain trait based on the allele. This means that one of the alleles will always dominate the other allele no matter what. Unless both the alleles are recessive. example: B will always reult in blue eyes whereas b will result in brown eyes... BB leads to blue eyes, Bb leads to blue eyes but bb will result in brown eyes (both alleles are recessive).