Shotgun sequencing
![In whole genome shotgun sequencing (top), the entire genome is sheared randomly into small fragments (appropriately sized for sequencing) and then reassembled. In hierarchical shotgun sequencing (bottom), the genome is first broken into larger segments. After the order of these segments is deduced, they are further sheared into fragments appropriately sized for sequencing.](/Images/godic/202502/10/Whole_genome_shotgun_sequencing_versus_Hierarchical_shotgun_sequencing2209.png")
![A BAC contig that covers the entire genomic area of interest makes up the tiling path.](/Images/godic/202502/10/Tiling_path2209.png")
In genetics, shotgun sequencing, also known as shotgun cloning, is a method used for sequencing long DNA strands. It is named by analogy with the rapidly expanding, quasi-random firing pattern of a shotgun.
The chain termination method of DNA sequencing (or "Sanger sequencing" for its developer Frederick Sanger) can only be used for fairly short strands of 100 to 1000 base pairs. Longer sequences are subdivided into smaller fragments that can be sequenced separately, and subsequently they are re-assembled to give the overall sequence. Two principal methods are used for this: primer walking (or "chromosome walking") which progresses through the entire strand piece by piece, and shotgun sequencing which is a faster but more complex process that uses random fragments.