Practice question

Yeast artificial chromosomes enable cloning of 100 kb to 1 megabase DNA, often maintained singly in yeast and shuttled to Escherichia coli for manipulation. However, characterization reveals significant instability. Because yeast recombination machinery acts on repetitive mammalian DNA, chimerism, internal deletions and rearranged inserts are common, sometimes affecting 20-50 percent of clones. Multiple YACs can coexist per cell and insert can be unstable during mitotic propagation. Therefore claim of complete stability without rearrangements is incorrect. Understanding limitations led to development of BACs and PACs offering greater structural fidelity for genome projects.