Bacterial Artificial Chromosome (BAC)
Definition
An F-plasmid-derived cloning vector capable of carrying 100-300 kb inserts stably in E. coli at one copy per cell. The Human Genome Project used BAC libraries as its primary substrate; BAC-derived sequence coordinates define the physical map positions of forensic STR loci.
- Abbreviation
- BAC
- Vector origin
- F-plasmid derived
- Insert capacity
- 100 to 300 kb
- Host organism
- E. coli, one copy per cell
- Forensic relevance
- Anchors physical map coordinates of STR loci
Common questions
Why does maintaining one copy per cell matter for a BAC vector?+
A single-copy-per-cell design keeps large inserts stable by minimising recombination between repeated copies of the same DNA within the host bacterium, which is important for cloning large genomic fragments without them rearranging or degrading before they can be sequenced or mapped.
How do BAC-derived coordinates connect to STR typing used in casework?+
The Human Genome Project's BAC-tiling path gave each genomic region a defined physical position, and forensic STR loci such as those in commercial multiplex kits are located relative to that same reference coordinate system, which is why locus nomenclature and chromosomal position in STR kit literature trace back to BAC-based mapping work rather than to the STR discovery itself.
Is BAC cloning still used directly in modern forensic DNA laboratories?+
Routine casework does not clone samples into BAC vectors; that work belongs to genome mapping and reference-sequence construction. Its relevance to forensic practice today is historical and referential, in that it underpins the reference genome coordinates that forensic loci are defined against.
Related terms
- Blue-White Screening (Alpha-Complementation)
- A colony selection method for pUC-family vectors in which intact lacZ-alpha produces functional beta-galactosidase that cleaves X-gal to a blue indigo product....
- Multiple Cloning Site (MCS)
- A short stretch of synthetic DNA containing a cluster of unique restriction sites, engineered into cloning vectors such as pUC19 and pBlueScript...
- Plasmid
- A small, circular, double-stranded DNA molecule that replicates autonomously inside a bacterial cell. Used as a cloning vector when equipped with a...
- RFLP (Restriction Fragment Length Polymorphism)
- The first DNA profiling method used in forensic casework, developed by Alec Jeffreys in 1984. Restriction enzymes cut DNA at specific sequences,...
- Sticky End (Cohesive End)
- A single-stranded overhang generated when two cuts on opposite strands of a DNA duplex are offset rather than directly opposite each other....
- Type II Restriction Endonuclease
- A bacterial enzyme that cleaves double-stranded DNA at a specific palindromic recognition sequence, generating fragments whose ends reflect the exact geometry of...