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 acid4 (replica plates numbered 1 to 4) with the following results: For colonies 1, 3, and 5, write '+' for the wild-type synthesis and '−' for the mutant synthesis of histidine and leucine.

Verified step by step guidance

1. Step 1: Understand the experimental setup. The yeast cells are exposed to EMS, a mutagen, and then plated on a complete medium where all necessary nutrients are provided.
2. Step 2: Recognize that the replica plates are used to test the ability of the colonies to grow on minimal medium, which lacks certain nutrients, or minimal medium supplemented with specific amino acids.
3. Step 3: Analyze the growth pattern of colonies 1, 3, and 5 on the replica plates. Growth on minimal medium indicates wild-type synthesis of the required nutrients, while lack of growth indicates a mutation affecting synthesis.
4. Step 4: Determine the synthesis capability for histidine and leucine for each colony. If a colony grows on minimal medium without supplementation, it synthesizes both amino acids ('+'). If it only grows on medium supplemented with histidine or leucine, it cannot synthesize that amino acid ('−').
5. Step 5: Record the synthesis status for histidine and leucine for colonies 1, 3, and 5 based on their growth patterns on the replica plates.

Key Concepts

Haploid Organisms

Haploid organisms, such as yeast, have a single set of chromosomes, which means they possess only one allele for each gene. This genetic simplicity allows for straightforward observation of mutations, as any change in phenotype directly reflects a change in genotype. In experiments, haploid yeast can be used to study gene function and the effects of mutagens like ethyl methanesulfonate (EMS).

Mutagenesis

Mutagenesis is the process by which the genetic information of an organism is changed, resulting in mutations. Ethyl methanesulfonate (EMS) is a chemical mutagen that induces point mutations, often leading to changes in amino acid sequences of proteins. Understanding mutagenesis is crucial for interpreting the effects of EMS on yeast colonies, particularly in relation to their ability to synthesize essential amino acids.

Amino Acid Synthesis Pathways

Amino acid synthesis pathways are biochemical routes through which organisms produce amino acids from simpler compounds. In yeast, the ability to synthesize amino acids like histidine and leucine is essential for growth on minimal media. The presence of mutations can disrupt these pathways, leading to a requirement for external sources of these amino acids, which is critical for analyzing the results of the experiment.