1. You wish to measure the reversion rate of a gal4 mutation in haploid yeast Th
ID: 268861 • Letter: 1
Question
1. You wish to measure the reversion rate of a gal4 mutation in haploid yeast The gal4 mutants are unable to grow when galactose is the only carbon source so you can detect revertants by plating on galactose plates. You inoculate each of 50 small tubes with 1 ml of galactose based medium and about 10 gal4 cells and incubate the tubes until they each contain about 2 x 107 cells. You then plate the contents of each tube on a single galactose plate, and count gal4+ colonies after incubation. Number of colonies on each plate: 2 0 0 3 0 2 123 0 1 0 0 27 1 3 0 1 0 1 0 2 a. Calculate the reversion rate of the gal4 mutation. b. Calculate the reversion frequency of the gal 4 mutationExplanation / Answer
Poisson distribution can be used to calculate mutation reversion rate of gal4 mutants.Mutation reversion rate refers to number of mutations per cell/division. This Po method refers to distributation rate of mutations that occur in parallel culture growth following a Poisson distribution.A luria-Delbruck fluctuation test can deteremine the rate.
The number of plates/sites, that did not have any revertants (or mutants) are 20 (ones where no revertent that is 0 is indicated).
The mutation rate "r" = h/N, wherein h = -ln (20/50) i.e = -ln(0.4) = 0.9162 and N is number of cells i.e 2*10^7 per ml * 1 ml , (also assuming 1 ml of culture is plated)
thus muatation rate = 0.916/2*10^7 = 0.458 * 10^-7 or 4.58*10^-8 mutations/cell division
Reversion frequency of gal 4 mutants can be calculated by ratio of number of mutants/ number of cells in a population.For each plate it would vary depending upon the number of colonies formed.
Related Questions
Navigate
Integrity-first tutoring: explanations and feedback only — we do not complete graded work. Learn more.