The ability to curl ones tongue is due to a dominant allele (T) while those who are homozygous recessive (tt) cannot roll their tongues. Unilateral deafness is also genetically determined as an autosomal dominant trait, with D=deaf and d= normal hearing. A woman who is heterozygous for both traits mates with a man who has normal hearing but cannot roll his tongue. What is the probability of their having a child who is a tongue-roller and deaf in one ear?