<P> In genetics, a genome - wide association study (GWA study, or GWAS), also known as whole genome association study (WGA study, or WGAS), is an observational study of a genome - wide set of genetic variants in different individuals to see if any variant is associated with a trait . GWASs typically focus on associations between single - nucleotide polymorphisms (SNPs) and traits like major human diseases, but can equally be applied to any other organism . </P> <P> When applied to human data, GWA studies compare the DNA of participants having varying phenotypes for a particular trait or disease . These participants may be people with a disease (cases) and similar people without the disease (controls), or they may be people with different phenotypes for a particular trait, for example blood pressure . This approach is known as phenotype - first, in which the participants are classified first by their clinical manifestation (s), as opposed to genotype - first . Each person gives a sample of DNA, from which millions of genetic variants are read using SNP arrays . If one type of the variant (one allele) is more frequent in people with the disease, the variant is said to be associated with the disease . The associated SNPs are then considered to mark a region of the human genome that may influence the risk of disease . </P>

In large scale genome-wide association studies in humans we look for