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

Key Concepts

Haploid Organisms

Haploid organisms, like yeast, have a single set of chromosomes, which means they possess only one allele for each gene. This simplifies genetic analysis since any mutation will directly affect the phenotype. In the context of the question, understanding haploidy is crucial for determining how mutations induced by EMS may manifest in the yeast colonies.

Mutagenesis

Mutagenesis refers to the process by which the genetic information of an organism is changed, resulting in mutations. Ethyl methanesulfonate (EMS) is a chemical mutagen that can induce point mutations in DNA. Recognizing how EMS affects yeast genetics is essential for interpreting the results of the experiment and understanding which colonies may exhibit unknown genotypes.

Replica Plating

Replica plating is a technique used to transfer colonies from one agar plate to another, allowing for the assessment of growth under different conditions. In this experiment, colonies are transferred to minimal medium to test for auxotrophy, which indicates whether they can synthesize certain amino acids. This method is key to determining if any colonies have unknown genotypes based on their growth patterns in the presence or absence of specific nutrients.