recombinant DNA
Suppose you cut a sentence out of one book and paste it into another so the two now read as a single passage. Recombinant DNA is the molecular version of that splice: a DNA molecule stitched together from pieces that originally came from different sources, so that sequences which never met in nature now sit side by side.
It is made by cutting DNA from two sources, often with the same restriction enzyme so the cut ends match, and then joining them with DNA ligase. A common arrangement is to insert a gene of interest into a plasmid or other vector, creating a single hybrid molecule that a host cell can take up and copy. Because the host treats this molecule as ordinary DNA, it reads and replicates the foreign sequence along with its own.
Recombinant DNA technology, developed in the early 1970s, is the foundation of modern molecular biology. It lets researchers isolate, multiply, and study individual genes, and it underlies the industrial production of proteins like insulin and growth hormone. The DNA itself is chemically identical to any other DNA — what is novel is the combination of sequences, not the molecule's nature.
A plasmid carrying a spliced-in human gene is recombinant DNA: part bacterial backbone, part human insert, fused into one continuous circle.
Two origins, one molecule — the defining feature of recombinant DNA.
The term refers to the recombined molecule itself; the laboratory method of making and using such molecules is often called recombinant DNA technology or, more broadly, genetic engineering.