The researchers looked at levels of RNA, which works as a messenger carrying out DNA's instructions, in samples of liver tissue that were collected in two separate studies. One study looked at samples from liver donors, and the other studied people who were undergoing gastric bypass surgery. The Mount Sinai team looked for markers called expression quantitative trait loci, or eQTLs, which are locations on the genome that regulate expression of certain proteins or RNAs. They used algorithms that matched these eQTL patterns to variations in DNA bases, extrapolating the DNA sequences. Schadt describes it as "hearing a symphony and deducing which instruments are in the orchestra, essentially unwinding the developmental process to trace tissue samples back to RNA and the gene that instructed it."