Question

You isolate three E. coli mutants that are unable to synthesize histidine. You amplify the gene responsible for the phenotype from the wildtype (WT) and mutant strains (1, 2, and 3) using PCR and run the PCR products on an agarose gel. Based on the results, which mutant is likely to have an deletion in the gene of interest? (The top of the gel is where the DNA was loaded - the negatively charged end) Wt 1 2 3

Answer 1

Gel electrophoresis is a technique used to separate DNA fragments according to their size. DNA samples are loaded into wells at one end of a gel, and an electric current is applied to pull them through the gel. DNA fragments are negatively charged, so they move towards the positive electrode. Thus largest fragments will be heavier and remain on the top and lighter fragments will move lastly and come to the bottom. On this basis fragment number 1 is lightest as it is moving very fast and is near the bottom so this fragment has suffered a deletion I.e loss of nucleotides.