Textbook Question
Using your knowledge of DNA repair pathways, choose the pathway that would be used to repair the following types of DNA damage. Explain your reasoning.
A cytosine that has been deaminated to uracil
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17. Mutation, Repair, and Recombination
Induced Mutations
1:43 minutesProblem 40b
Textbook Question
Common baker's yeast (Saccharomyces cerevisiae) is normally grown at 37°C, but it will grow actively at temperatures down to approximately 25°C. A haploid culture of wild-type yeast is mutagenized with EMS. Cells from the mutagenized culture are spread on a complete-medium plate and grown at 25°C. Six colonies (1 to 6) are selected from the original complete-medium plate and transferred to two fresh complete-medium plates. The new complete plates (shown) are grown at 25°C and 37°C. Four replica plates are made onto minimal medium or minimal plus adenine from the 25°C complete-medium plate. The new plates are grown at either 25°C or 37°C and the growth results are shown.
Classify the nature of the mutations in colonies 1, 2, and 5.
Verified step by step guidance1
Step 1: Understand the experimental setup. The yeast cells were mutagenized using EMS (ethyl methanesulfonate), which induces point mutations. The colonies were grown under different conditions (temperature and media) to observe their growth patterns. The goal is to classify the mutations based on these observations.
Step 2: Analyze the growth results for colonies 1, 2, and 5. Look at the growth patterns on complete medium at 25°C and 37°C, as well as on minimal medium and minimal medium plus adenine at both temperatures. This will help determine if the mutations affect temperature sensitivity or nutrient requirements.
Step 3: Determine if the mutations are temperature-sensitive. If a colony grows at 25°C but not at 37°C, it suggests a temperature-sensitive mutation affecting a gene required for growth at higher temperatures.
Step 4: Assess nutrient requirements. If a colony grows on minimal medium plus adenine but not on minimal medium alone, it indicates an adenine auxotrophy mutation, meaning the colony requires adenine supplementation to grow.
Step 5: Classify the mutations. Based on the growth patterns, assign the nature of the mutations for colonies 1, 2, and 5. For example, a colony that is temperature-sensitive and adenine auxotrophic would have both types of mutations. Use the data provided to make these classifications.
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Key Concepts
Here are the essential concepts you must grasp in order to answer the question correctly.
Mutagenesis
Mutagenesis is the process by which the genetic information of an organism is changed, resulting in a mutation. In this context, the wild-type yeast is treated with EMS (ethyl methanesulfonate), a chemical mutagen that induces random mutations in the DNA. Understanding mutagenesis is crucial for analyzing the resulting phenotypes of the yeast colonies, as it helps to identify whether the mutations are beneficial, neutral, or harmful.
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Haploid Organisms
Haploid organisms, like the yeast Saccharomyces cerevisiae, have a single set of chromosomes, which simplifies the analysis of genetic mutations. In haploids, any mutation will directly affect the phenotype since there is no second allele to mask its effects. This characteristic makes haploid yeast an excellent model organism for studying gene function and mutation effects, particularly in experiments involving mutagenesis.
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Phenotypic Analysis
Phenotypic analysis involves observing and classifying the physical and functional traits of organisms resulting from their genetic makeup. In this experiment, the growth of yeast colonies at different temperatures and on various media allows researchers to determine the nature of mutations present in colonies 1, 2, and 5. By comparing growth patterns, researchers can infer whether mutations are related to temperature sensitivity or nutrient utilization, which is essential for classifying the mutations.
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