Final answer:
Scientists use genetic markers, such as antibiotics and enzymes, to determine which cells have been successfully transformed. This allows them to identify and select transformed cells from non-transformed cells.
Step-by-step explanation:
In genetic engineering, scientists use markers to determine which cells have been successfully transformed. These markers can be antibiotics or enzymes that the transformed cells either respond to or produce. For example, an antibiotic resistance gene can be inserted into the vector, and transformed cells that have taken up the gene will be resistant to the antibiotic.
Another method is reverse genetics, where scientists start with a specific DNA sequence and try to determine the phenotype it produces. Reporter genes can also be attached to genes of interest, allowing researchers to easily monitor their expression.
By using these genetic markers, scientists can identify and select the transformed cells from the non-transformed cells to create a cDNA library or determine gene function.