Fig. 1. An overview of current and emerging technologies for genomic sequencing. Sequencing can be classified into four main strategies: in vitro cloning, in vivo cloning, amplification and mass spectrometry, and single-molecule approaches. The mass spectrometry and single-molecule approaches are still either very specialized or in the developmental stages, although mass spectrometry methods such as the MassArray method is commonly used for single nucleotide polymorphism (SNP) analysis (Jurinke et al., 2002). In vivo cloning followed by Sanger sequencing is the workhorse method of most current genome sequencing projects. The in vitro cloning technologies can be further divided into methods that employ sequencing by synthesis, such as the 454 and Solexa methods, or those that use hybridization and ligation of oligonucleotides, such as MPSS (massively parallel signature sequencing) and polony methods.