The aim of the study was to compare the function of the MKT1 gene alleles in strains of the yeast Saccharomyces cerevisiae with different genetic backgrounds. MKT1 gene influences processes of several RNA molecules and through this affects several cellular processes. We chose 20 segregants that were obtained from a cross between two strains of yeast S. cerevisiae, which all share the same allele of gene MKT1. Using CRISPR-Cas9 method we first deleted the MKT1 gene in these segregants, and in the next step inserted the MKT1 allele from the other parental strain. We wanted to determine the difference in growth between variants with different MKT1 alleles on media with added chemicals that activate the TOR signalling pathway. In order to achieve this, we cultivated the three different variants of each segregant on in the presence of caffeine or rapamycin and compared their resistance. The variants with the MKT1BY and mkt1Δ alleles grew comparably in all conditions. From this result we concluded that the Mkt1BY protein variant is non-functional. On the medium with caffeine there was no difference in the growth between segregants in half of the segregants, but in the other half the variant with the MKT1AWRI allele was less resistant to caffeine. From this result we hypothesized that MKT1 gene influences caffeine resistance in combination with another gene. On the medium with rapamycin the segregants were grouped into 3 different groups. From this result we concluded that the resistance against rapamycin is a complex, i.e. polygenic trait. To determine which and how many genes influence resistance against rapamycin and caffeine, the segregants’ genomes should be sequenced and the SNP distribution among segregants analyzed.