Genome wide association study for T2D-related loci Genome wide association study for T2D-related loci Appropriate study groups are selected from the general population (1). For example, a group of individuals who have T2D (2) and a group of individuals who are healthy to act as controls (3). These groups must be matched as far as possible in terms of their constitution to avoid confounding effects – for example, matched for gender, ethnicity, smoking, socioeconomic status, education and so on. For each individual, thousands of SNPs across the genome are genotyped (4), and then the overall allele frequencies are compared between the two groups for SNPs across each chromosome (5). Each spot on the graph represents one SNP at a known location on a particular chromosome. The expectation is that, for the vast majority of SNPs, the MAF will be similar between the two groups. However, where there is a difference, either a significantly higher (6) or significantly lower (7) MAF in the affected group, this identifies a specific chromosome location which may play a role in T2D. Note that the actual variants which either predispose to obesity or protect from T2D may be close to the relevant SNPs (i.e. genetic linkage) rather than the SNPs themselves being causative or protective. Maria Jackson et al. Essays Biochem. 2018;62:643-723 ©2018 by Portland Press Ltd