Linkage versus association studies

Professor Allen Moore describes the differences between linkage and association studies, which are low- and high-resolution techniques used to search for candidate genes.

Linkage is actually looking at physical segments of the genome that are associated with given traits. Association studies go from the other direction, saying, 'given different pieces of the genome, can we then look for different traits that are associated with those different segments of genome?' So we know that individuals don't have the same genetic makeup. They have the same DNA, but the DNA has different sequences or is expressed differently, and that's what causes differences among different individuals. So the question is that if we have a trait, particularly a disease trait, can we find and associate that with differences among individuals in the population? So a linkage study is just saying, 'can we say that there is an association between pieces of the DNA and a trait of interest?' Association studies are saying, 'what are the differences we see?' in order to find differences in the traits, particularly disease traits, among different individuals.