Author summary Loss of heterozygosity (LOH) is a common genetic process in diploid organisms, where one allele of a gene on one chromosome is replaced by a duplicate copy of the allele from the other chromosome. Although LOH occurs frequently as diploid cells divide, our understanding of its effects is limited, because most studies focus on events that have already been filtered by natural selection. To fully capture both the beneficial and detrimental effects LOH may generate, we engineered a mutant library of the baker’s yeast Saccharomyces cerevisiae containing with randomly induced LOH events. Unlike traditional methods, our approach allowed us to measure the immediate consequences of these changes across the genome before they were lost to natural selection. By testing these strains across various environments, we found that while LOH is often deleterious or neutral, it can be a source of beneficial genetic variation depending on the environmental context. We observed a high prevalence of trade-offs associated with LOH, where strains gained an advantage in one environment at the cost of fitness in others. These findings suggest that LOH is capable of facilitating rapid adaptation as a form of short-sighted evolution and specialization.


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PLOS (Public Library of Science)