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PCR |
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polymerase chain reaction (PCR)Laboratory technique used to make numerous copies of specific DNA segments quickly and accurately. These are needed for various experiments and procedures in molecular biology, forensic analysis (DNA fingerprinting), evolutionary biology (to amplify DNA fragments found in ancient specimens), and medicine (to diagnose genetic disease or detect low viral counts). Invented by Kary Mullis, PCR requires a DNA template (as little as one molecule) to copy, nucleotides to build the copies, and the enzyme DNA polymerase to catalyze the formation of bonds between the nucleotide monomers. Each three-step cycle (separating the two strands of the DNA double helix, marking the ends of the segment to be copied, and catalyzing the formation of bonds), which takes only minutes to complete, doubles the number of DNA strands present in the reaction medium. Repetition of this cycle many times results in an exponential increase in the amount of DNA. PCR (cell and molecular biology) How to thank TFD for its existence? Tell a friend about us, add a link to this page, add the site to iGoogle, or visit webmaster's page for free fun content. |
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However, your advice that a negative HIV test is grounds for having unsafe sex with a partner is erroneous. 1) In a subsample of participants who had never tested positive for the virus before the survey, only 54% said that they had had an HIV test within the previous year; the rest had been tested in the more distant past or had never been tested at all. We tried to retest cases with an indeterminate HIV test result. |
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