Question: 2. In an E. coli mapping experiment, a cross is made between an Hfr strain that is a+ b+ d+ in ge…

2. In an E. coli mapping
experiment, a cross is made between an Hfr strain that is
a⁺ b⁺ d⁺ in genotype and an
F^– strain that is a^– b^–
d^– in genotype. Interrupted-mating studies show that
b⁺ enters the recipient strain last. The b⁺
recombinants are then tested for the presence of the a⁺
and d⁺ alleles. The following data were obtained (4
marks):

   a⁺ b⁺ d⁺ 326

   a^– b⁺ d⁺ 2

   a⁺ b⁺ d^– 14

   a^– b⁺ d^– 58

Total: 400

a) What is the gene order (show your reasoning)?

b) What are the frequencies of recombination between each pair
of genes?

c) Draw a map, showing map distances (in map units) between
genes.