Week 5 laboratory reflection - UV mutagenesis

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Indiana University, Bloomington *

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Biology

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Feb 20, 2024

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Name: Laboratory Reflection: UV mutagenesis Instructions: Make sure to scroll through the entire document to answer all questions. It would also help with grading if you put your typed answers in a different (but readable) color font . Save and upload your completed assignment to the associated assignment page on Canvas. It is the student’s responsibility to confirm that the correct file was submitted to Canvas by the due date. 1. (0.5pts) Transfer the data you collected on page 9 of your laboratory protocol packet to the tables below (type in your values). Your group’s data: Time of irradiation (sec.) # colonies on SC medium # colonies on SD medium 0 428 1 20 279 91 40 261 146 60 304 135 80 203 64 100 99 48 120 65 11 Your Lab Section’s data (obtained by the end of lab period from your AI): Time of irradiation (sec.) # colonies on SC medium # colonies on SD medium 0 463 2 20 478 51 40 317 106 60 308 102 80 208 75 100 253 41 120 188 38 2. (1pt) To show the effect of UV light exposure on the survival rate of the yeast (data from SC plates), you need to express the data as the percentage of cells that survived (i.e. percent survival). Calculate the percent survival of both your lab group’s data and your lab section’s data and fill your answers in the table below. Show your work for at least one of your calculations. 1 Hint: To calculate this percentage we will use the “0 sec” plate as a control, and assume that 100% of the cells on the “0 sec” plate survived. So, your calculation for each time of UV exposure is: percent survival relative to control plate = (# colonies on plate) _ * 100 (# colonies on “0 sec” plate) Consider the following: What if the calculations suggest that some plates have more than 100%

3. (1pt) To determine the effect of UV yeast exposure on the rate of mutation to the TRP1+ phenotype, you need to calculate the mutation rate (i.e. percent mutation). Calculate the % mutation for both your lab group’s data and your lab section’s data and fill your answers in the table below. Show your work for at least one of your calculations. 2 Hint: We need to take several things into account when calculating mutation rates… 1. The concentration of cells in the original yeast culture was unknown. 2. The survival rate of the yeast cells is different at different levels of UV exposure. 3. The concentration of the original culture used to inoculate the SD plates was 10,000x greater than the concentration of the culture used to inoculate the SC plates 4. The actual counted numbers of colonies present on the SD plates varied. First, we’ll address points 1 and 2. The number of yeast colonies you counted on the SC plates for each time of UV exposure gives you an estimate of the number of cells that should have survived that amount of UV exposure, and takes into account the concentration of the original culture. To consider point 3, we have to take the SC plate colony count and multiply it by 10,000, to estimate the number of surviving cells on each SD plate. Remember, most of those cells plated on SD media couldn’t reproduce and form colonies because they couldn’t make their own tryptophan. Points 1, 2, and 3 allow us to calculate approximately how many cells survived on each SD plate. Then we just need to figure out what proportion of these surviving cells also mutated to the TRP1+ phenotype. This is just the number of colonies you counted on each SD plate (point 4). So, your calculation for each time of UV exposure is: % mutation = (number of colonies counted on SD plate) _ * 100 (number of colonies counted on SC plate x 10,000) Time of UV exposure % survival (lab group data) % survival (lab section data) 0 seconds 1% 1% 20 seconds 65.18% 96.86% 40 seconds 60.98% 68.46% 60 seconds 70.13% 66.52% 80 seconds 47.43% 44.92% 100 seconds 23.13% 54.64% 120 seconds 22.20% 40.60%

4. Create four separate graphs from your data (a-d). All 4 graphs must include the two types of data compiled for this lab: your lab group’s data and your lab section’s data. Each graph must have a descriptive title—do not use the term ‘versus.’ Each graph must have both data types clearly identified with a key and/or described in the figure caption. Each graph must have a brief figure caption to describe the figure. If needed, see additional graphing resources linked within this assignment page on Canvas. a. (1pt) Graph the SD plate data as # of colonies vs irradiation time Hint: Your graph should have time of UV exposure (seconds) on the horizontal (x) axis, and number of colonies on the vertical (y) axis. [Insert graph (a) with figure caption here] 3 Note on figure captions: A complete figure contains both an image and a caption. Together, these two parts should provide enough information that a reader can understand the data presented without referring to the text. A figure caption should contain a concise description of the graphic allowing a reader to understand the figure.  The information contained within the caption should include a description of the graph (similar to a title), a brief statement of the methods necessary to understand the figure, statistical information, if applicable.  The caption should never begin with the words “Graph of...” or “Figure of...”  Example: Figure 1. Mean weight of golden-mantled ground squirrels was 150 g greater than that of thirteen-lined ground squirrels prior to hibernation. Although both species lost weight during hibernation, golden-mantled ground squirrels exhibited greater weight loss. Time of UV exposure % mutation (lab group data) % mutation (class data) 0 seconds 0.002336% 0.000043% 20 seconds 0.003262% 0.001067% 40 seconds 0.005594% 0.003344% 60 seconds 0.004441% 0.003312% 80 seconds 0.003153% 0.003606% 100 seconds 0.004848% 0.001621% 120 seconds 0.001692% 0.002021%

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0 20 40 60 80 100 120 0 20 40 60 80 100 120 140 160 Comparison SD plates over an Irridation of Time Number colonies on SD medium Average Number colonies on SD medium UV Exposure Number of Colonies The time of UV exposure increased in seconds on the SD plates and the number of colonies increased for only a certain amount of time (about 40 seconds) before decreasing. b. (1pt) Graph the SC plate data as # of colonies vs irradiation time [Insert graph (b) with figure caption here] 0 20 40 60 80 100 120 0 100 200 300 400 500 600 Comparison of SC plates over an Irridation of Time Number colonies on SC medium Average Number colonies on SC medium UV Exposure Number of Colonies The time of UV exposure increased in seconds on the SC plates and the number of colonies decreased. 4

c. (1pt) percent survival vs. irradiation time for the SC plates. Hint: You calculated % survival in question 2. [Insert graph (c) with figure caption here] 0 seconds 20 seconds 40 seconds 60 seconds 80 seconds 100 seconds 120 seconds 0% 20% 40% 60% 80% 100% 120% Survival Rate of Yeast over an Irridation of Time % survival (lab group data) % survival (lab section data) UV Exposure Surival Percentage The time of UV exposure increased in seconds and the percent survival increased for about 20 seconds before decreasing d. (1pt) percent mutation vs. irradiation time Hint: You calculated % mutation in question [Insert graph (d) with figure caption here] 0 seconds 20 seconds 40 seconds 60 seconds 80 seconds 100 seconds 120 seconds 0 0 0 Rate of Mutation for yeast over an Irridation of Time % mutation (lab group data) % mutation (class data) UV Exposure Mutation Percentage The time of UV exposure increased in seconds, the percent of mutations varied slightly between the two sets of data. In both groups the time of UV exposure increased in seconds but in our 5

group the mutation percentage increased for about 40 seconds before decreasing at around 80 seconds and then increasing for another 20 seconds before decreasing. In the class data the mutation percentage in creased for about 40 seconds, then levelled off for about 40 seconds, then decreased at the 80 second mark, and finally levelling off at 100 seconds. 5. (1pt) What is the effect of UV irradiation on the overall survival of yeast cells based on data presented in question 4c? Why would UV-induced mutations impact the survival of cells? Overall, the effect of JV irradiation on the survival of yeast cells is negative. The longer the cells are exposed to UV, the more their survival rate decreases. UV induced mutation impact the survival of cells because UV radiation can inhibit DNA replication and cause damage to the DNA. 6. (1pt) What is the effect of UV on cells carrying trp1-289 ? Did UV induce a genetic change in cells carrying the trp1-289 allele and how do you know? Be specific. UV effect cells carrying trp1-289 by damaging or changing the cell’s DNA. It induces a genetic change in the cells carrying this allele and this can lead to cell death. In the graphs there is an increase and then a decrease in cells the longer they are exposed to UV. This can tell us that the increase means that while the UV is mutating and changing the cell’s DNA, it is still able to repair and replicate to survive. The decrease means that too much damage has occurred to the DNA so it cannot repair itself and this can lead to cell death. 7. (0.5pts) Examine Figure A (i.e. the SD plate data as # of colonies vs irradiation time). Why does the curve for the reversion of trp1-289 show the shape that it does? Recall that you have done two experiments (one with SC media and one with SD media), each of which allows you to interpret what UV does to yeast cells. The exposure of UV to the cells leads to a decrease in the cells viability and increase in changes to DNA. This can cause the cells to be slower in their work and make it so that it may take the cell more time to repair itself. This slowed down rate will make it harder for the cells to keep up with the damage caused to them and will eventually lead to the cells dying. 8. (1pt) Write a brief summary of how your data (collected by you and your lab partner(s)) compares to the larger data set of the entire lab section. In what ways are they similar or different? What is the benefit of comparing your data to a larger data set? Somethings that I noticed from the data collection was that in both data sets there were some outliers that could have skewed the results. This may be caused by human error, and it may be due to the time between sterilization and spreading of the yeast being too little or there was misinterpretation of the procedure that may have led to errors in the experiment itself. Overall, 6

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the trends in both data sets seemed to be similar which can lead to the assumption that there were not great errors done within the experiment. Even though the results may not have seemed accurate, comparing them to the larger data set allowed us to see taht in the end they did match those of the bigger group. 7

Week 5 laboratory reflection - UV mutagenesis

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