A stable cell line is generated when transfected DNA undergoes integration into a chromosome by nonhomologous recombination. Cells that stably express selectable (e.g., antibiotic-resistant) markers are also likely to have incorporated other DNA sequences. This phenomenon, in which physically unlinked genes are assembled into a single integrated array and expressed in the same transfected cell, is known as "cotransfection." Resistance to antibiotics has proven to be effective in selecting cotransfectants and, in some cases, as a driver for gene amplification.
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