The Frequency of Survivorship in Heterozygous Diploids of Cdc13-1exo1Δ Mutants of S. <i>cerevisiae</i> Is One Survivor Cell in 72 Cells/Generation at 36°C

Abstract

Telomeres cap ends of eukaryotic chromosomes prevent them from degradation and ensure genomic stability. Cdc13 is an essential telomere recruitment and maintenance protein. A temperature-sensitive point mutation in cdc13 gene leads to telomere impairment, giving rise to cdc13-1 mutants that suffer lethality at enhanced temperatures. Deleting Exo1 gene from these mutants, however, leads to the emergence of temperature-tolerant mutants called survivors. Yeasts are known to exist as either diploids or haploids. These yeast genotypes generate survivors. The frequency of survivorship in the haploid genotype is one cell in 104 cells/generation at 36˚C, however, the frequency at which they emerge in their diploid counterparts at the same temperature is not known. In this study, we investigated the frequency of Survivorship in heterozygous diploids of cdc13-1exo1Δ mutants of S. cerevisiae at 36˚C. Diploids were constructed by mating haploid strains of opposite mating type cdc13-1 exo1:LEU strains with strains of cdc13-1 exo1:HIS. The crosses were 1296 × 3181, 2561 × 3182, 1296 × 3182 and 2561 × 3181. Genetic markers and phenotypic appearance were considered while mating the mutant cells. Using a stick, a smear of one haploid strain was made on each YEPD plate labelled C2, C8, C9, D1, D14, and D15. A smear of another opposite mating type was made on the previous strain. They were mixed and allowed to mate overnight, before culturing on media lacking Luecine and Histidine (-L and -H).

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

“…Diploid species are known to inherit randomly, a copy of the allele from each of their parent [15], during segregation of traits and could be homozygous, having two same copies of allele of a gene, or heterozygous, having two different copies of allele of a gene. However, one allele in heterozygous diploids could be dominant, and the phenotype expressed in the offspring, or recessive, with the phenotype receded in the offspring [25,26]. Co-dominance exists, though, where no allele has a complete dominance in the phenotype of the offspring [15].…”