Essential Genetics 6th Edition by Daniel Hartl

Exercise 14

In the yellow-fever mosquito, Aedes aegypti, a dominant gene DDT for DDT resistance (DDT is dichlorodiphenyltrichloroethane, a long-lasting insecticide) and a dominant gene Dl for Dieldrin resistance (Dieldrin is another long-lasting insecticide) are known to be in the same chromosome. A cross was carried out between a DDT-resistant strain and a Dieldrin-resistant strain, and female progeny resistant to both insecticides were testcrossed with wildtype males. Among the progeny, 99 were resistant to both insecticides, 88 were resistant to DDT only, 89 were resistant to Dieldrin only, and 106 were sensitive to both insecticides.
(a) Are DDT and Dl alleles of the same gene? How can you tell?
(b) Are DDT and Dl linked?
(c) What can you deduce about the genetic positions of DDT and Dl along the chromosome?