Week 5 laboratory reflection - UV mutagenesis

Name: Clayton Swartz 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 0 784 4 20 160 0 40 11 0 60 3 0 80 0 0 100 0 0 120 0 0 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 1227 1 20 806 38 40 482 24 60 503 12 80 432 10 100 107 8 120 176 3 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 100% 100% 20 seconds 20.3% 65.7% 40 seconds 1.4% 39.3% 60 seconds 0.4% 41% 80 seconds 0% 35.2% 100 seconds 0% 8.7% 120 seconds 0% 14.3%

0 20 40 60 80 100 120 140 0 100 200 300 400 500 600 700 800 900 Colonies on SC Medium (Group Data) X axis = Time of Irradiation Y axis = # of colonies on SC Medium b. (1pt) Graph the SC plate data as # of colonies vs irradiation time [Insert graph (b) with figure caption here] 0 20 40 60 80 100 120 140 0 0.5 1 1.5 2 2.5 3 3.5 4 4.5 Colonies on SD Medium (Group Data) X axis = Time of Irradiation Y axis = # of colonies on SC Medium c. (1pt) percent survival vs. irradiation time for the SC plates. Hint: You calculated % survival in question 2. 4

0 20 40 60 80 100 120 140 0 20 40 60 80 100 120 % Survival vs Irradiation Time X Axis: Irradiation Time Y Axis: % Survival d. (1pt) percent mutation vs. irradiation time Hint: You calculated % mutation in question 0 20 40 60 80 100 120 140 0 0 0 0 0 0.01 0.01 Mutation Rate vs Irradiation Time X axis: Irradiation time Y axis: % Mutation 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? The UV radiation killed a lot of cells, but during the 40 second time a lot of them mutated. If their mutation gives them a survival advantage, then they are more resistant to radiation but aren’t immune. That is why they still almost all die at 120 seconds. 5