Identifying and characterizing the genetic variants that impact human traits, ranging from disease susceptibility to variability in personality measures, is one of the central objectives of human genetics. Ultimately, this aim will be achieved by examining the relationship between interesting traits and the whole genome sequences of many individuals. Although whole genome resequencing of thousands of individuals is not yet feasible, geneticists have long recognized that good progress can be made by measuring only a relatively modest number of genetic variants in each individual. This type of “incomplete” information is useful because data about any set of genetic variants in a group of individuals provides useful information about many other unobserved genetic variants in the same individuals.
