Q18 - Predicting Spore Genotype Frequencies from Yeast Meiosis

In its life cycle, baker’s yeast Saccharomyces cerevisiae has haploid and diploid generations. The haploid has alpha-type and a-type mating types and grows independently. When alpha-type cells and a-type cells meet, they undergo sexual conjugation and become diploid (a/alpha-type) cells. When the nitrogen source is depleted, the diploid cells undergo meiosis and form four spores (two a-type cells and two alpha-type cells) inside the cell. The haploid XY-1A strain (genotype: a, ura3, leu2) requires uracil and leucine for growth, and the XY-2B strain (genotype: alpha, his3, leu1) requires histidine and leucine for growth. A diploid XY-3C strain (a/alpha, ura3/URA3, leu2/LEU2, LEU1/leu1, HIS3/his3) was obtained by sexual mating of the XY-1A strain and the XY-2B strain. Out of 160 spores obtained from the XY-3C strain, approximately how many spores can grow on a medium containing uracil but not leucine/histidine? The genes of the mating type, the URA3, the LEU2, the LEU1, and the HIS3 are all present on different chromosomes.

Using the information and data, determine which of the statements are true or which are false.

Question reproduced from IBO 2020, Theoretical Exam 2, licensed under CC BY-NC-SA 4.0 - attributed to the International Biology Olympiad. Open the full exam PDF · Community solutions (unofficial)