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:

Are there any colonies for which genotype information cannot be determined? If so, which colony or colonies?

Verified step by step guidance

1. Step 1: Understand the experimental setup. A wild-type haploid yeast culture was mutagenized with EMS and plated on complete medium. Six colonies were selected and replica plated onto four different media: minimal medium, minimal + histidine, minimal + arginine, and minimal + leucine. Growth or no growth on these plates indicates whether the colonies require supplementation for specific amino acids.
2. Step 2: Analyze growth on the minimal medium (Plate 1). Colonies that grow on minimal medium are prototrophic (do not require supplementation), while those that do not grow are auxotrophic (require supplementation). From the image, colonies 1 and 4 grow on minimal medium, so they are prototrophic; colonies 2, 3, 5, and 6 do not grow, indicating auxotrophy.
3. Step 3: Analyze growth on minimal + histidine (Plate 2). Colonies that grow here but not on minimal medium are likely histidine auxotrophs. Colonies 1 and 4 grow here (consistent with prototrophy), colony 3 grows here but not on minimal medium, indicating it is a histidine auxotroph. Colony 2 does not grow here, so it is not rescued by histidine.
4. Step 4: Analyze growth on minimal + arginine (Plate 3). Colonies 1, 2, and 4 grow here. Colony 2 grows here but not on minimal or minimal + histidine, indicating it is an arginine auxotroph. Colonies 3, 5, and 6 do not grow here.
5. Step 5: Analyze growth on minimal + leucine (Plate 4). Colonies 1, 4, and 5 grow here. Colony 5 grows only on minimal + leucine, indicating it is a leucine auxotroph. Colony 6 does not grow on any plate except complete medium, so its genotype cannot be determined from this data because it does not grow on any minimal or supplemented medium.

Key Concepts

Replica Plating Technique

Replica plating is a method used to transfer colonies from one plate to multiple plates with different media. It helps identify mutants by comparing growth patterns on selective versus non-selective media, revealing nutritional requirements or auxotrophies.

Auxotrophic Mutations in Yeast

Auxotrophic mutations cause yeast cells to lose the ability to synthesize specific nutrients, requiring supplementation for growth. By testing growth on minimal media plus specific amino acids, one can determine which nutrient the mutant cannot produce.

Interpreting Growth Patterns for Genotype Determination

Growth or no growth on minimal and supplemented media indicates the genotype of yeast colonies. Colonies growing only on supplemented media are auxotrophs for that nutrient, while those growing on minimal media are prototrophs. Ambiguous or inconsistent growth complicates genotype identification.