Figure 1.

Design of a GWAS for height. Many individuals are collected and are measured for their height. Genotyping assays are then performed on the DNA for each individual to identify the genetic variants each individual carries. Each variant is then tested for correlation with height in the study population. Shown on the top right panel are sample box-and-whisker plots for a genetic variant that is not associated for height. As can be seen, the average height of individuals with the three different genotypes at this variant are approximately the same. On the bottom right are sample box-and-whisker plots for a genetic variant that is associated with height. Here, it can be seen that individuals who carry one or two copies of the A allele of this variant have decreased height. Note the small effect of this variant (0.5-cm reduction in height per A allele), which in reality would be a very strong effect for a GWAS-associated variant. Also, the associated variant is not deterministic, as the distributions of heights among the three genotypes are largely overlapping.