The polymerase chain reaction makes copies of DNA and it doesn’t, strictly speaking, need T. acquaticus in order to work. Instead, what it needs is a polymerase, a type of enzyme involved in building and repairing DNA. Scientists take DNA from an organism that contains a segment of DNA they want to copy, and mix it with polymerase, a bunch of loose nucleotides to build DNA from, and short strands of nucleotides, called primers, that show the polymerase where to start building and where to stop. Then, it’s just a matter of heating and cooling. Heat the mixture up, and the DNA separates into two strands. Cool it down and the primers latch on. Heat it up again, and the polymerases go to work, turning loose nucleotides into DNA copies. If you run the cycles of heating and cooling over and over and over, you can exponentially multiply the copies of your target DNA. One becomes two. Two becomes four. Four becomes eight. In a matter of hours, you can create millions.
— Read on m.nautil.us/issue/44/Luck/from-a-pink-squiggle-to-the-human-genome-project