5) Why is unlikely that a man who is a PTC nontaster and a woman who is a PTC nontaster will have a child who is a PTC taster?

Phenylthiocarbamide (PTC), also known as phenylthiourea (PTU), is an organosulfur thiourea containing a phenyl ring. ... The ability to taste PTC is often treated as a dominant genetic trait, although inheritance and expression of this trait are somewhat more complex.

Explanation:nability to taste PTC is sometimes described as an autosomal recessive trait: persons with the TT or Tt genotypes have the "taster" phenotype, persons with the tt genotype have the "non-taster" phenotype. The "non-taster" phenotype is therefore described as a "recessive" trait.