Figure 5.

Elevated Rates of Loss of Heterozygosity

(A) The length distribution of homozygous segments, in bins corresponding to 50-kb increments, shows an excess of long homozygosity tracts above 300 kb in hydroxyurea and rapamycin (Kolmogorov-Smirnov test, p < 0.01). Ancestral haploid isolates are used to compare a set of in silico diploid genomes to evolved diploid isolates. Only unrelated isolate backgrounds were included.

(B) Background- and environment-dependent rates of loss of heterozygosity were measured in a fluctuation assay by loss of the URA3 marker. Resistant colonies growing in 5-fluororotic acid (5-FOA+) indicate loss of the marker. Based on the number of 5-FOA+ colony-forming units (CFUs), the mean number of LOH events are estimated using the empirical probability-generating function of the Luria-Delbrück distribution (Supplemental Experimental Procedures). The locus-specific LOH rates are shown, given by the mean number of LOH events divided by the total number of cells in YPD. Error bars denote the upper and lower 95% confidence intervals. LOH rates were elevated in hydroxyurea compared with the control environment and manifested background-dependent effects between the parents and their hybrid.

See also Figure 4.