3 You discover a mutant yeast strain that cannot grow when provided with pyruvate as its sole carbohydrate, although it grows normally when given glucose as a carbon energy source; you call this the Pyr- trait. Wild-type yeast can grow well using either carbon source; you designate this the Pyr+ trait. You suspect that the mutant yeast have defective mitochondria.
A. Why is mitochondrial function critical for growing on pyruvate?
B. You want to determine whether the mutation responsible for the Pyr- trait is carried in the nuclear or mitochondrial genome. Your experiment is to mate Pyr- haploid cells to Pyr+ haploid cells and examine segregation of the trait in the progeny. After mating, the hybrid diploid cells can grow on pyruvate (Pyr+). You send these diploid cells through meiosis and examine the four haploid cells generated from a single diploid cell. If the mutation is in mitochondrial DNA, will the four haploid cells probably be all Pyr-, all Pyr, or a combination? What if the mutation is in nuclear DNA?