Shotgun sequencing is an approach used to decode an organism's genome by shredding it into smaller fragments of DNA which can be sequenced individually. The sequences of these fragments are then ordered, based on overlaps in the genetic code, and finally reassembled into the complete sequence. The 'whole genome shotgun' method is applied to the entire genome all at once, while the 'hierarchical shotgun' method is applied to large, overlapping DNA fragments of known location in the genome.