DNA collection methods are distinguished primarily on the basis of cost and sample quality, with a generally inverse relationship between the two. The cheapest way of obtaining DNA samples is to use buccal swabs, brushes or cotton buds that collect cells from the inside of the cheek. These have a long shelf life and can be mailed in large numbers very cheaply. However, they have the distinct disadvantage of yielding the lowest quality, most degraded genomic DNA because the collected cells have been sloughed off by the cheek epithelium and the DNA has been partially degraded by natural processes. Although GWAS using buccal swab samples have been reported, these samples generally are not of the quality needed for the most intensive contemporary applications, like GWAS and sequencing. The enhanced sample quality requirements for these applications argues strongly for the use of higher quality sampling methods.
