What type of vector was primarily used for cloning in the Human Genome Project?

The type of vector primarily used for cloning in the Human Genome Project was the bacterial artificial chromosome, or BAC.

BACs are engineered DNA molecules based on the bacterial F plasmid. They can carry large inserts of human DNA—typically around 150,000 to 350,000 base pairs—while being stably maintained and copied inside Escherichia coli. This made them well suited to the HGP’s clone-by-clone sequencing strategy.

Researchers first fragmented human DNA and inserted the pieces into BACs. The resulting clones were mapped and arranged into overlapping physical contigs, then individual clones were sequenced and assembled computationally. Large, stable inserts reduced rearrangement problems and helped laboratories coordinate work across particular chromosome regions.

Cosmids and ordinary plasmids can also carry foreign DNA, but their inserts are generally smaller. Yeast artificial chromosomes can carry even larger fragments and were important in earlier genome mapping, yet BACs became the principal large-insert cloning system for the public HGP. Modern whole-genome shotgun and long-read methods largely reduced the need for BAC libraries.