You study leucine biosynthesis in a strain of /Salmonella typhimurium/. You have identified four new leucine auxotrophic mutants in a mutagenesis screen. You label them /leuA/, /leuB/, /leuC/, and /leuD/.

Preliminary mapping of the mutant loci indicates that they all group to one side of the /ala3/ locus. As part of your research, you decide to map all four loci relative to the /ala3/ locus using bacteriophage cotransduction.

Part A – Calculating cotransduction frequencies To calculate cotransduction frequencies, you use bacteriophage to transduce DNA from wild-type donor bacteria to recipient bacteria of various genotypes. For each experiment, you select for recipient cells that are prototrophic for alanine by plating cells on a master plate containing minimal medium + leucine, which allows all /leu/ genotypes to grow. You then replica plate each master plate on minimal medium without leucine.

Use the data shown below to calculate the frequency at which each /leu/ locus cotransduces with /ala3/ ^+. Complete the table by dragging the correct label to the appropriate location. Labels may be used once, more than once, or not at all.

Part B – Rough mapping using cotransduction frequencies Using the cotransduction frequencies from Part A, create a rough map of the /leuA/, /leuB/, /leuC/, and /leuD/ loci relative to the /ala3/ locus. Place the four loci on the map by dragging the correct label to the appropriate location. Two loci map to approximately the same location, so use a label with both loci for that location. (Note: The map is not drawn to scale.)