دانلود کتاب Test No. 481 : genetic toxicology : saacharomyces cerevisiae, miotic recombination assay

This assay may be used to measure mitotic recombination (gene conversion or crossingover) in yeast, a eukaryotic micro-organism. Crossing-over is generally assayed by the production of recessive homozygous colonies or sectors produced in a heterozygous strain, whereas gene conversion is assayed by the production of prototrophic revertants produced in an auxotrophic heteroallelic strain carrying two different defective alleles of the same gene. Stationary or growing cells are exposed to the test chemical (solid, liquid, vapour or gas) with and without an exogenous mammalian metabolic activation system for up to 18 hours at 28°-37°C with shaking. After incubation for 4-7 days at 28°-30°C in the dark, plates are scored for survival and the induction of mitotic recombination. At least five adequately spaced concentrations of the test substance should be used. A minimum of 3 replicate plates should be used per concentration for the assay of prototrophs produced by mitotic gene conversion and for viability. If the first experiment is negative, then a second experiment should be carried out using stationary phase cells. If the first experiment is positive, it is confirmed in an appropriate independent experiment. NB. This Test Guideline will be deleted on 2nd April 2014.  Read more...