UC San Diego

Vector-borne diseases pose a significant health threat to millions. Genetic modification through CRISPR/Cas9-based gene drive technologies may be able to solve this problem by rapidly spreading disease resistance throughout vector populations. However, the long-term effects of active gene drive elements at evolutionary scales has yet to be extensively explored. To address this issue, we constructed S. cerevisiae strains that express both Cas9 and gRNA, Cas9 and no gRNA, or neither Cas9 nor gRNA. We founded replicate populations and propagated these over 1000 generations. From whole-population, whole-genome sequences, we identified changes in allele frequency in each population. By comparing the numbers of alleles to appear or fix in each population, we find evidence of higher mutation rates in strains expressing Cas9 nuclease. In parallel, we directly measure the mutation rate differences due to gene drive or Cas9 alone. Our work underscores the need to control CRISPR/Cas9 activity to limit unintended effects in natural populations.