Dear student,
A yeast artificial chromosome (YAC) is a vector used to clone DNA fragments larger than 100 kb and up to 3000 kb. The major advantage of using artificial chromosomes such as YACs is that it can carry much larger DNA fragments than ordinary plasmids.
BAC (Bacterial artificial chromosome): It is an artificially constructed vector containing origin of replication & selectable marker for identification. It is capable of carrying large DNA fragments and can replicate easily inside a bacterial cell.
Regards