**1.1 Background and history of bacterial artificial chromosome (BACs)**

BACs were first developed as a large insert cloning system to facilitate the construction of DNA libraries to analyze genomic structure (Shizuya, Birren et al. 1992). BACs are derived from a fertility plasmid (F-plasmid) found in the *Escherichia coli.* BACs can clone extremely large DNA molecules, ranging from 150-700kb,and averaging 350 kb. Another advantage of BACs over other cloning technologies is its stability in cell culture and ease of manipulation. Because some recombinant viruses were too large to be generated by traditional techniques, BAC technology was developed to carry out genetic and functional studies of viruses, especially herpesvirus. (Warden, Tang et al. 2011). From the time when BACs emerged a decade ago, their application have grown intensely and have benefited the research community in many fields, such as sequencing of the human genome, *in vitro* transgenesis, genomic fingerprinting, and even to vaccine development.
