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PCR

PCR copies a chosen piece of DNA many times. Each cycle separates the strands with heat, primers attach when it cools, and DNA polymerase builds a new strand. From one molecule there are two, then four, and so on. After n cycles there are two to the power of n copies, if you started with one molecule and every copy succeeds. A small trace of DNA is therefore enough, for example from a crime scene. PCR makes the copies. It does not sort them, and it does not cut them.

2^n

copies after n cycles, from one molecule

Symbols

$n$	number of cycles
$2$	doubling each cycle

Example

Ten cycles from one DNA molecule.

Copies: $2^{10} = 1024$ .

If you start with more molecules, you multiply by that number at the end.

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← From DNA to mRNA · Restriction enzyme →

Part of Biology 2: Biotechnology.