Complex sentence: Often the dominant allele codes for a functional protein whereas the recessive allele does notof alleles (genotypes) are possible: "RR", "Rr", and "rr".
Split into simpler sentences: Often the dominant allele codes for a functional protein whereas the recessive allele does not. In this case, three combinations of alleles (genotypes) are possible: "RR", "Rr", and "rr".