In recent years, techniques for manipulating prokaryotic as well as eukaryotic DNA have witnessed a remarkable development. This has allowed breakage of a DNA molecule at two desired places to isolate a specific DNA segment and then insert it in another DNA molecule at a desired position. The product thus obtained is called recombinant DNA and the technique often called genetic engineering. Using, this technique we can isolate and clone single copy of a gene or a DNA segment into an indefinite number of copies, all identical. This became possible because, bacteria, phages and plasmids reproduce in their usual manner even after insertion of foreign DNA, so that the inserted DNA will also replicate faithfully with the parent DNA. This technique is called 'gene cloning'. With this technique, genes can be isolated, cloned and characterized, so that the technique has led to significant progress in all areas of molecular biology. More recently, polymerase chain reaction (PCR) involving a thermostable DNA polymerase (Taq polymerase) has been used to obtain millions of copies of a DNA segment of choice. This PCR technique may eventually replace gene cloning in certain areas of research in the field of genetic engineering. In this section, we will discuss some details of these techniques involving production of recombinant DNA, and the cloning and amplification of DNA segments. The use of these techniques will be discussed in the next few topics of genetics on ePlantScience.com.