17. Mutation, Repair, and Recombination

Types of Mutations

17. Mutation, Repair, and Recombination

Types of Mutations

2:47 minutes

Problem 28a

Textbook Question

Yeast are single-celled eukaryotic organisms that grow in culture as either haploids or diploids. Diploid yeast are generated when two haploid strains fuse together. Seven haploid mutant strains of yeast exhibit similar normal growth habit at 25°C, but at 37°C, they show different growth capabilities. The table below displays the growth pattern.

Hypothesize about the nature of the mutation affecting each of these mutant yeast strains, including why strains B and G display different growth habit at 37°C than the other strains.

Verified step by step guidance

Understand the problem: The question involves analyzing the growth patterns of mutant yeast strains at different temperatures (25°C and 37°C). The goal is to hypothesize the nature of the mutations and explain why strains B and G behave differently at 37°C compared to the others.

Step 1: Recall that yeast can exist as haploid or diploid cells. Mutations in haploid yeast strains can directly affect their phenotype because there is no second allele to mask the mutation. This means that any mutation affecting growth at 37°C is likely due to a single defective gene in each strain.

Step 2: Analyze the growth patterns at 25°C and 37°C. Since all strains grow normally at 25°C, the mutations likely affect temperature-sensitive genes. These genes may encode proteins that are functional at lower temperatures but become misfolded or non-functional at higher temperatures (37°C).

Step 3: Hypothesize the nature of the mutations. For strains B and G, their different growth habits at 37°C suggest that the mutations in these strains may affect different pathways or genes compared to the other strains. For example, strain B might have a mutation in a gene involved in heat shock response, while strain G might have a mutation in a gene critical for cell division at higher temperatures.

Step 4: Consider genetic interactions. If strains B and G display unique growth patterns, it is possible that their mutations are in genes that interact with other cellular pathways differently than the mutations in the other strains. This could explain their distinct behavior at 37°C.

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Key Concepts

Here are the essential concepts you must grasp in order to answer the question correctly.

Haploidy and Diploidy

Haploidy refers to cells that contain a single set of chromosomes, while diploidy indicates cells with two sets. In yeast, haploid strains can mate to form diploid cells, which can undergo meiosis to produce haploid spores. Understanding the difference between these two states is crucial for analyzing genetic mutations and their effects on growth under varying conditions.

Temperature Sensitivity in Mutants

Temperature sensitivity in mutant strains refers to the phenomenon where certain mutations affect the organism's ability to grow or function at specific temperatures. In this case, the yeast strains exhibit normal growth at 25°C but show varied growth capabilities at 37°C, suggesting that the mutations may impact protein stability or enzymatic activity at higher temperatures.

Genetic Mutations and Phenotypic Expression

Genetic mutations are changes in the DNA sequence that can lead to alterations in an organism's phenotype, or observable traits. The differences in growth habits of strains B and G at 37°C compared to other strains may indicate specific mutations that affect metabolic pathways or stress responses, highlighting the relationship between genotype and phenotype in response to environmental changes.

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