Consider two linked autosomal genes. The dominant allele C of the first gene causes cataracts of the eye, whereas its recessive allele produces normal eyes. The dominant allele P causes polydactyly (an extra finger) whereas its allele (p) produces a normal number of fingers. A man with cataracts and normal fingers marries a woman with polydactyly and normal eyes. Their son has both polydactyly and cataracts and he marries a woman with neither trait. What is the probability that their first child will have cataracts and polydactyly?