Gene duplication is an important evolutionary mechanism and, as result , many cases are known where species has two nearly identical genes. Suppose there are two genes, A and B , that specify production of the same enzyme. An abnormal phenotype results only if an individual does not make any of that enzyme. What ratio of normal vs abnormal progeny would result from a mating between two parents of the genotype AaBb , where A and B represent alleles that specify production of the enzyme, and a and b are alleles that do not.