Cloning is used to make many copies of a gene of interest.

A hummingbird gene is inserted into a plasmid (cloning vector) from E. coli with a restriction enzyme. The plasmid contains the ampR gene, which makes E. coli cells resistant to the antibiotic ampicillin.

It also contains the lacZ gene encoding β-galactosidase; this enzyme digests the sugar X-gal to form a blue product.
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