The 1,000 Genomes Project, which began in 2008, was an international effort to create a detailed and publicly accessible catalog of human genetic variation to support medical studies aimed at exploring genetic contributions to disease. Project scientists sequenced the entire genomes of 2,504 individuals from around the world—more than the 1,000 originally planned. The Project extended the results of the International HapMap Project, a prior effort at cataloging human genetic variation that ran from 2002 through 2010. Whereas the HapMap identified common genetic variants, meaning specific DNA sequences present in five percent or more of individuals in a population, the 1,000 Genomes Project identified genetic variants present in as few as one percent of individuals in a population. By assembling a larger catalog of DNA sequence variation than had previously existed, the 1,000 Genomes Project paved the way for researchers to more precisely locate disease-related genetic variation passed from parent to child.

A genome-wide association study, or GWAS, is a method for identifying variations in DNA that may contribute to the development of a particular trait, such as a disease. A GWAS relies on identifying statistical correlations between many, often thousands of, DNA markers and a particular trait. Scientists employ GWASs to try to identify the genetic contributions to complex traits, such as common human diseases. Complex traits are ones that scientists suspect are the result of multiple genes and environmental inputs acting together, in contrast to simple, Mendelian disorders that result primarily from the disturbance of a single gene. The genetic variants identified through a GWAS typically account for only a small proportion of the expected genetic contribution to a complex trait, which scientists refer to as the missing heritability problem. Since 2006, scientists have conducted thousands of GWASs aimed at identifying the genetic contributions to complex traits and have identified many thousands of genetic variations that correlate with those traits, although as of 2025, because of the missing heritability problem and other limitations, the concrete contributions of GWASs to medicine have so far been modest.