Design and practice of educational experiments on genetic epistasis.

Genetic epistasis is a fundamental concept in genetics that describes how interactions between genes determine phenotypic traits. To enhance students' understanding and practical application of genetic epistasis, this experiment is designed and conducted using gene mutations in the adenine biosynthesis pathway of Saccharomyces cerevisiae (baker's yeast). S. cerevisiae is a classic model organism for genetic teaching experiments. In its adenine biosynthesis pathway, a mutation in the ADE2 gene leads to the accumulation of the intermediate 5'-phosphoribosylaminoimidazole (AIR), causing the cells to appear red. However, if a gene upstream of ADE2 in the adenine biosynthesis pathway (such as ADE8) is defective, the red phenotype of yeast will disappear. Conversely, a defect in a gene downstream of ADE2 (such as ADE1) does not alter the red phenotype. Therefore, ADE8 is epistatic to ADE2. In this experiment, the CRISPR-Cas9 genome editing technology is employed, allowing students to perform single knockout of ade2Δ, as well as double knockouts of ade2Δade8Δ and ade2Δade1Δ in S. cerevisiae. By observing the phenotypic changes in yeast mutants from white to red and back to white, students gain a profound understanding of the basic genetic theory of how genes determine phenotypes and the concept of epistasis in gene interactions. This experiment also enables students to master fundamental yeast genetic techniques, significantly enhancing their ability to design and conduct experiments in real research environments. This is of great significance for their future research work and academic development.