Ultra-violet light is produced by high-energy wave frequencies just outside of the visible spectrum. This light energy can interfere with the bonds which comprise the backbone of DNA by exciting the electrons in these atoms—leading to conformational changes which cause base-pair bonds to be broken, shifted, or replaced, causing genetic mutations, or abnormalities in the typical phenotypic expression of an organism. The purpose of this lab was to understand more about ultraviolet light as an agent of mutagenesis and become familiar with the manipulation of the single-celled fungus Saccharomyces cerevisiae. Through a series of experiments, the effects of varying degrees of UV radiation exposure on cultures of yeast were assessed for cultures
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This explains why there were no colonies in the SD plate which had no radiation exposure time. Small amounts of radiation would produce some mutations, but not so many that mutations are likely to occur in multiple locations in the genome and have lethal effects. Therefore, the number of colonies that were present decreased with increasing radiation exposure time. The SD plates which spent the longest under the lamp likely had too many mutations overall and one or more mutation for each cell proved lethal. The largest number of SD colonies survived in Plate 2 (20 seconds), but the highest % of mutation occurred in Plate 5. The % mutation rate for each UV exposure time considers the number of cells that had expressed beneficial mutations necessary for survival in an “incomplete” medium compared to the number of colonies that would be expected to survive at that given irradiation time in an SC plate multiplied by a factor of 10,000. The data in figure 2 supports my original hypothesis that an increasing radiation exposure time would lead to an increasing percentage of (beneficial) mutations, but after a certain length of time, the increasing quantity of mutations would become detrimental to the viability of the cells. A previously conducted experiment by Svihla et al. (1960) showed that the irradiation of cells with ultraviolet light lead to effects such as mutation and cell death which further supports the results that I
This explains why there were no colonies in the SD plate which had no radiation exposure time. Small amounts of radiation would produce some mutations, but not so many that mutations are likely to occur in multiple locations in the genome and have lethal effects. Therefore, the number of colonies that were present decreased with increasing radiation exposure time. The SD plates which spent the longest under the lamp likely had too many mutations overall and one or more mutation for each cell proved lethal. The largest number of SD colonies survived in Plate 2 (20 seconds), but the highest % of mutation occurred in Plate 5. The % mutation rate for each UV exposure time considers the number of cells that had expressed beneficial mutations necessary for survival in an “incomplete” medium compared to the number of colonies that would be expected to survive at that given irradiation time in an SC plate multiplied by a factor of 10,000. The data in figure 2 supports my original hypothesis that an increasing radiation exposure time would lead to an increasing percentage of (beneficial) mutations, but after a certain length of time, the increasing quantity of mutations would become detrimental to the viability of the cells. A previously conducted experiment by Svihla et al. (1960) showed that the irradiation of cells with ultraviolet light lead to effects such as mutation and cell death which further supports the results that I