You have isolated two petite mutants, pet1 and pet2, in Saccharomyces cerevisiae. When pet1 is mated with wild-type yeast, the haploid products following meiosis segregate 2:2 (wild type : petite). In contrast, when pet2 is mated with wild type, all haploid products following meiosis are wild type. To what class of petite mutations does each of these petite mutants belong? What types of progeny do you expect from a pet1 × pet2 mating?

Verified step by step guidance

1. Understand the problem: The question involves two petite mutants (pet1 and pet2) in Saccharomyces cerevisiae and their inheritance patterns. Petite mutants in yeast can be classified into three categories: nuclear mutations, neutral petites, and suppressive petites. The goal is to determine the class of mutation for each mutant and predict the progeny from a pet1 × pet2 mating.
2. Analyze the pet1 mutant: When pet1 is mated with wild-type yeast, the haploid products segregate 2:2 (wild type : petite). This indicates that the mutation is likely a nuclear mutation because nuclear mutations follow Mendelian inheritance, leading to a 2:2 segregation pattern during meiosis.
3. Analyze the pet2 mutant: When pet2 is mated with wild-type yeast, all haploid products are wild type. This suggests that pet2 is a neutral petite mutation. Neutral petites have defective mitochondrial DNA, but their mitochondrial DNA is not transmitted to the progeny, resulting in all wild-type offspring when crossed with wild type.
4. Predict the progeny from a pet1 × pet2 mating: Since pet1 is a nuclear mutation and pet2 is a neutral petite, the progeny will inherit the nuclear mutation from pet1 and the wild-type mitochondrial DNA from pet2. The expected progeny will segregate 2:2 (wild type : petite) because the nuclear mutation from pet1 follows Mendelian inheritance.
5. Summarize the findings: pet1 belongs to the class of nuclear petite mutations, while pet2 belongs to the class of neutral petite mutations. From a pet1 × pet2 mating, the progeny will segregate 2:2 (wild type : petite) due to the Mendelian inheritance of the nuclear mutation from pet1.

Key Concepts

Mitochondrial Genetics

Mitochondrial genetics refers to the study of genes located in the mitochondria, which are inherited maternally. In yeast, petite mutations often arise from defects in mitochondrial DNA, affecting cellular respiration and energy production. Understanding the inheritance patterns of these mutations is crucial for determining the type of petite mutants, as they can be classified based on their ability to produce viable offspring when crossed with wild-type strains.

Meiosis and Segregation

Meiosis is a specialized form of cell division that reduces the chromosome number by half, resulting in haploid gametes. The segregation of alleles during meiosis follows Mendel's laws, where alleles segregate independently into gametes. In the case of pet1, the 2:2 segregation indicates that it is likely a nuclear mutation affecting mitochondrial function, while the all-wild-type progeny from pet2 suggests it may be a mutation that does not complement pet1 or is linked to mitochondrial inheritance.

Complementation Testing

Complementation testing is a genetic technique used to determine whether two mutations that produce a similar phenotype are in the same gene or in different genes. In the context of the petite mutants, mating pet1 and pet2 can reveal whether they belong to the same genetic pathway affecting mitochondrial function. If the offspring from a pet1 × pet2 cross show a mix of petite and wild-type phenotypes, it indicates that the mutations are in different genes, while all wild-type offspring would suggest they are in the same gene.