A gene encodes an enzyme, and there are two alleles of the gene. 65 units of the enzyme are required for the wild-type phenotype. Less than 65 units of the enzyme results in a mutant phenotype. One allele (A1) produces 50 units of the enzyme. A null allele (A2) produces 0 units of the enzyme. What is the phenotype of the A1A2 heterozygote