In diploid yeast strains, sporulation and subsequent meiosis can produce haploid ascospores, which may fuse to reestablish diploid cells. When ascospores from a segregational petite strain fuse with those of a normal wild-type strain, the diploid zygotes are all normal. Following meiosis, ascospores are petite and normal. Is the segregational petite phenotype inherited as a dominant or a recessive trait?

Verified step by step guidance

1. Understand the problem: The question involves determining whether the segregational petite phenotype in yeast is inherited as a dominant or recessive trait. This requires analyzing the inheritance pattern during meiosis and sporulation.
2. Step 1: Recall that diploid yeast cells undergo meiosis to produce haploid ascospores. In this case, the segregational petite strain is crossed with a wild-type strain, and the resulting diploid zygotes are all normal. This suggests that the wild-type allele compensates for the petite phenotype in the diploid state.
3. Step 2: After meiosis, the ascospores are observed to segregate into petite and normal phenotypes. This indicates that the petite phenotype is not completely masked in the haploid state, and its inheritance can be analyzed through the segregation pattern.
4. Step 3: Analyze the segregation pattern of the ascospores. If the petite phenotype is recessive, we would expect a 1:1 ratio of petite to normal ascospores, assuming Mendelian inheritance. This is because the diploid zygote would be heterozygous (wild-type/petite), and meiosis would segregate the alleles into equal proportions.
5. Step 4: If the petite phenotype were dominant, all ascospores would exhibit the petite phenotype, as the presence of one petite allele would be sufficient to express the trait. However, the observation of both petite and normal ascospores suggests that the petite phenotype is inherited as a recessive trait.

Key Concepts

Diploid and Haploid Cells

Diploid cells contain two sets of chromosomes, one from each parent, while haploid cells have only one set. In yeast, diploid strains can undergo meiosis to produce haploid ascospores. Understanding the difference between these cell types is crucial for analyzing inheritance patterns and phenotypic expressions in the context of the question.

Sporulation and Meiosis

Sporulation is the process by which yeast cells undergo meiosis to produce spores, specifically ascospores in this case. This process is essential for sexual reproduction in yeast and leads to genetic variation. Recognizing how sporulation and meiosis contribute to the generation of different phenotypes helps in determining the inheritance of traits.

Dominant and Recessive Traits

Dominant traits are expressed in the phenotype even when only one copy of the allele is present, while recessive traits require two copies for expression. In the context of the question, understanding whether the segregational petite phenotype is dominant or recessive is key to predicting the outcome of the crosses between different yeast strains and their resulting phenotypes.