A co transduction experiment is carried out with three tightly linked genes, a+ b+ and c+, using a recipient strain of genotype a- b- c-. Among a+ b- transductants, 14% are also c+. Among a+ c+ transductants, 83% are also b+. And among b+ c+ transductants, 18% are also a+. Which of the three genes is in the middle?