In molecular biology, amplification is a process by which a nucleic acid molecule is enzymatically copied to generate a progeny population with the same sequence as the parental one. The most widely used amplification method is polymerase chain reaction (PCR). The result of a PCR amplification of a segment of DNA is called an “amplicon.” Nucleic acids can also be amplified in an isothermal reaction involving a reverse transcriptase, which copies RNA→DNA, and a DNA-dependent RNA polymerase, which transcribes DNA→RNA. Isothermal amplification does not generate double-stranded DNA, and it is mainly used for copying RNA. Ligase-based methods, including the so-called ligase chain reaction (LCR), can be also used for specific DNA or RNA amplification. A fourth general method for nucleic acid amplification involves cloning the selected DNA molecule into bacterial or eukaryotic cells, allowing them to reproduce, and collecting the amplified DNA.