A wild-type culture of haploid yeast is exposed to ethyl methanesulfonate (EMS). Yeast cells are plated on a complete medium, and 6 colonies (colonies numbered 1 to 6) are transferred to a new complete medium plate for further study. Four replica plates are made from the complete medium plate to plates containing minimal medium or minimal medium plus one amino acid (replica plates numbered 1 to 4) with the following results:

Identify the colonies that are auxotrophic (mutant). What growth information leads to your answer?

검증된 단계별 안내

Understand the problem: Auxotrophic mutants are yeast cells that cannot synthesize a specific compound (e.g., an amino acid) required for growth. These mutants will not grow on minimal medium unless the missing compound is provided. The goal is to identify which colonies are auxotrophic based on their growth patterns on the replica plates.

Analyze the experimental setup: The wild-type yeast culture was exposed to EMS, a mutagen that induces random mutations. Colonies were grown on complete medium (which contains all necessary nutrients) and then transferred to minimal medium (which lacks specific nutrients) and minimal medium supplemented with individual amino acids.

Interpret the growth data: Examine the growth patterns of the colonies on the replica plates. Colonies that grow on complete medium but fail to grow on minimal medium are likely auxotrophic. Further, if a colony grows on minimal medium supplemented with a specific amino acid, it indicates that the colony is auxotrophic for that amino acid.

Identify auxotrophic colonies: Compare the growth results across the replica plates. Colonies that fail to grow on minimal medium but grow on minimal medium supplemented with a specific amino acid are auxotrophic for that amino acid. Record these colonies and the corresponding amino acid deficiencies.

Summarize the findings: List the colonies identified as auxotrophic and specify the amino acid(s) they require for growth. Explain how the growth patterns on the replica plates led to this conclusion, emphasizing the role of minimal medium and supplemented amino acids in identifying the mutants.

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주요 개념

질문에 올바르게 답하기 위해 반드시 이해해야 하는 핵심 개념들은 다음과 같습니다.

Auxotrophy

Auxotrophy refers to the inability of an organism to synthesize a particular compound required for its growth, often due to mutations in genes involved in metabolic pathways. In yeast, auxotrophic mutants cannot grow on minimal media unless specific nutrients, such as amino acids, are provided. Identifying auxotrophic colonies involves observing their growth patterns on different media.

Ethyl Methanesulfonate (EMS)

Ethyl methanesulfonate (EMS) is a chemical mutagen that induces mutations in DNA by alkylating bases, leading to errors during DNA replication. This process can result in various mutations, including point mutations that may affect metabolic functions. Understanding the role of EMS is crucial for analyzing the resulting phenotypes of yeast colonies after exposure.

Replica Plating

Replica plating is a technique used to transfer colonies from one agar plate to another, allowing for the comparison of growth under different conditions. This method helps identify mutants by observing which colonies can grow on minimal media versus those that require additional nutrients. It is essential for determining the auxotrophic status of the yeast colonies in the experiment.