Linkage and association studies

Professor James Potash describes the difference between linkage and association studies, which are two ways of locating candidate genes. These are discussed in reference to bipolar disorder,

There are two major approaches to looking for candidate genes in bipolar disorder; the one that has been focused on the most is the gene-mapping approach, which is a hypothesis-free approach. Part of the reason that’s so attractive is because there has been so little that we’ve understood about the pathophysiology of the illness, of the way the illness unfolds in the brain, that we’ve thought that if we can from a hypothesis-free approach go directly to the gene it would be a huge advance. Linkage was the original way to go about that; that was a very low resolution way to screen the genome, looking for regions where there might be bipolar disorder genes. We are now at a much higher resolution approach that’s referred to as whole genome association, where you can look at seven hundred thousand to a million different places in the genome all at once; that’s the state of the art right now.