Researchers have used a lineage tracking method to characterize both the genetic basis and the fitness effects of hundreds of independent adaptive mutations in a laboratory evolution experiment of Saccharomyces cerevisiae. A previous study identified 25,000 lineages that gained an adaptive mutation within the first 168 generations of evolution. Now, the authors produced a comprehensive genotype-to-fitness map by isolating 4,800 colonies from the 88th generation — a point at which most adaptive lineages are likely to carry single adaptive mutations — and determining their barcodes. DNA barcode frequencies were monitored in pooled clones over the short term to measure the fitness of each clone. High-throughput genome sequencing of hundreds of known adaptive clones with varied fitness, as well as neutral clones, was performed to build a comprehensive genotype-to-fitness map of adaptation-driving mutations, highlighting two particular classes of adaptive mutations that drive early evolution.