Artificial chromosome vectors for cloning large DNA segments

We know that in plasmids, sequences upto 10-15kb; in lambda (λ)phage, sequences upto 22kb and in cosmids sequences upto 40kb can be cloned. Yeast artificial chromosome vectors (YACs), allow cloning of sequences that are several hundred kilobase pairs long. These long molecules of DNA which may rarely represent whole chromosomes can be cloned in yeast by ligating them to vector sequences that allow their propagation as linear artificial chromosomes. These long DNA molecules can be generated and allow construction of comprehensive libraries (with large DNA segments) in microbial hosts. These vectors along with other yeast plasmid vectors are shown in Figure 39.11.