We designed a screen to identify conditional mutants of S. cerevisiae in which the secretory system was defective. Suppose we were successful in identifying 12 mutants.
Describe the crosses you would perform to determine the number of different genes represented by the 12 mutations.

Verified step by step guidance

1. Step 1: Begin by crossing each of the 12 mutants with a wild-type strain of S. cerevisiae. This will ensure that the mutations are recessive and can be analyzed in subsequent steps. Observe the phenotypes of the resulting diploid strains to confirm that the secretory defect is recessive.
2. Step 2: Perform pairwise crosses between the 12 mutant strains to create diploid strains. For each cross, observe whether the diploid strain exhibits the mutant phenotype or the wild-type phenotype.
3. Step 3: Apply the concept of complementation testing. If two mutants complement each other (i.e., the diploid strain exhibits the wild-type phenotype), it indicates that the mutations are in different genes. If the diploid strain exhibits the mutant phenotype, the mutations are likely in the same gene.
4. Step 4: Organize the results of the complementation tests into groups based on which mutants complement each other. Each group represents a distinct gene involved in the secretory system.
5. Step 5: Count the number of groups formed from the complementation tests. This number represents the total number of different genes represented by the 12 mutations.

Key Concepts

Mutant Analysis

Mutant analysis involves studying organisms with specific mutations to understand gene function. In this context, identifying conditional mutants of S. cerevisiae helps researchers determine how these mutations affect the secretory system. By analyzing the phenotypes of these mutants, scientists can infer the roles of the affected genes.

Genetic Crosses

Genetic crosses are experimental breeding techniques used to study inheritance patterns and gene interactions. To determine the number of different genes represented by the 12 mutations, one would perform crosses between the mutants and analyze the offspring's phenotypes. This helps in identifying whether the mutations are in the same gene or in different genes.

Complementation Testing

Complementation testing is a method used to determine if two mutations that produce similar phenotypes are in the same gene or in different genes. By crossing two mutants and observing the phenotype of the offspring, researchers can assess whether the mutations complement each other (indicating different genes) or fail to complement (indicating the same gene). This is crucial for understanding the genetic basis of the identified mutants.