Estimation of the frequency of double LOH events in yeasts

Genomes contain mutations that can alter the performance of cells, particularly increasing the malignancy of cancer cells. In diploid organisms, the mutated gene is often heterozygous, the other and non-mutated variant is present and sufficient to maintain gene functionality. This protection can vanish in aberrant cell divisions, in which chromosomes or their parts containing healthy genes are lost or replaced by the mutated ones. Using a simple and tractable model eukaryote, the budding yeast, we show here that multiple (at least double) loss of heterozygosity events are much more common than expected. This may facilitate adaptive evolution or tumor progression when more than one change is needed to break constraints on further development.