Thermal Tolerance Phenotype in Cdc13-1 Exo1 Heterozygous Diploids of S. Cerevisiae Is a Dominant Trait

Abstract

Background: Telomeric DNA is found at the end of eukaryotic chromosomes, where they play a role in protecting the chromosome and the integrity of the genome of the organism through the activity of telomerase. Saccharomyces cerevisiae exists in two genotypes: haploid and diploid. Temperature sensitive point mutation on the cdc13 gene of each genotype and deletion of exo1 gene (cdc13-1Exo1 mutants) give rise to mutant survivors at enhanced temperatures. The mode of inheritance of the thermal tolerance allele in the heterozygous diploid genotype is not known. Materials and Methods: We constructed diploids by mating temperature sensitive haploid strains of opposite mating type cdc13-1 exo1: LEU with temperature resistant strains of cdc13-1 exo1::HIS. The crosses were 1296x3182 (D) and 2561x3181 (C). Using a sterile stick, smear of one haploid strain was made on each YEPD plates labelled C2, C8, C10, D4, D10, and D113. A smear of another opposite mating type was made on the previous strain. They were mixed and allowed to mate for six hours, before culturing on media lacking Luecine and Histidine (–L and –H) to purify and confirm that they are diploids. After confirmation, a loop full aliquot of the diploids were streaked on sterile media lacking leucine and histidine (-L, -H) and on YEPD and cultured at 370C to check thermal tolerance and number of viable colonies from each diploid crosses in (cfu). Result: The heterozygous diploid D thrived at the enhanced temperature of 370C and there is a significant difference in the yield of viable colonies by the D diploids when compared to the yield of the C diploids with P-value of 0.05. Conclusion: The growth of diploid D10 as shown in plate 3.1 establishes that, temperature resistant allele inherited by cdc13-1 exo1heterozygous diploids is a dominant phenotype, and its mode of inheritance is dominant as the heterozygous diploid thrived at the enhanced temperature of 370C.