molecular cloning
When biologists say they cloned a gene, they do not mean they made a whole copy of an animal. They mean they made many identical copies of one piece of DNA. Molecular cloning is the process of taking a single DNA fragment and producing a large, pure population of it inside living cells.
The classic recipe has a few steps. A DNA fragment is joined to a vector to make a recombinant molecule; that molecule is introduced into host cells, usually bacteria, by transformation; the cells are grown so that each one passes the vector to all its descendants; and finally the colonies carrying the desired insert are identified and selected. Because every cell in a colony descends from one founder, all the copies of the cloned DNA are identical.
Cloning gives researchers something precious: a renewable, pure supply of a specific DNA sequence to sequence, mutate, express, or study. While PCR can now amplify DNA in a test tube without cells, cell-based molecular cloning remains essential when you need the DNA maintained, replicated faithfully over time, or expressed as a protein in a living host.
A single bacterium carrying a recombinant plasmid grows overnight into a colony of millions, each cell holding an identical copy of the cloned gene.
One founder cell, one colony, millions of identical DNA copies.
Molecular cloning copies a DNA fragment, not an organism. It is unrelated to reproductive cloning (as in Dolly the sheep), which copies a whole individual from a single cell.