Answer: (cC)
Explanation: Curl (C) is governed by a change in one of the genes responsible for a structural protein in hair (keratin). The mutation again involves the substitution of a single nucleotide—this time, a T (thymine) is substituted for a C (cytosine). The substitution is believed to affect folding of the completed protein, leading to curled or wavy hair. Dogs with straight hair have two copies of the straight form of the gene (cc); dogs with wavy hair have one copy of the straight form of the gene and one copy of the curly form (Cc); dogs with curly hair are homozygous for the curly mutation (CC).