In a bacterial culture in which all cells are unable to synthesize leucine (leu^
ID: 224814 • Letter: I
Question
In a bacterial culture in which all cells are unable to synthesize leucine (leu^-) a potent mutagen is added, and the cells are allowed to undergo one round of replication. At that point, samples are taken, a series of dilutions is made, and the cells are plated on either minimal medium or minimal medium containing leucine. The first culture condition (minimal medium) allows the growth of only leu^+ cells, while the second culture condition (minimal medium with leucine added) allows growth of all cells. The results of the experiment are shown. What is the rate of mutation at the locus associated with leucine biosynthesis? Express your answer using two significant figures.Explanation / Answer
Answer:
Growth on minimal medium with 10-1 dilution of sample: 24 colonies
Growth on minimal medium+leucine with the sample dilution of 10-7: 3 colonies
Mutation rate is determined as the number of mutant cells divided by the total number of cells.
So, total number of cells in the original sample on minimal medium with 10-1 dilution = 24/10-1 = 240
Total number of cells in the original sample on minimal medium with 10-7 dilution = 3/10-7 = 3 * 107
Rate of mutation = 240/3 * 107 = 80 * 10-7 = 8 * 10-6 (The cells had undergone 1 round of replication)
So, the rate of mutation at the locus associated with leucine biosynthesis = 8 * 10-6/2 = 4 * 10-6