Which of the following is a limitation on theuse of PCR to detect and isolate ge

Question

Which of the following is a limitation on theuse of PCR to detect and isolate genes?
a. The sequence at the beginning and end of the DNA to be amplifiedmust be known
b. It also produces copies of sequences beyond the 5' and 3' end ofthe desired sequence
c. It cannot be used to amplify genomic DNA, only cloned DNA.
d. It will amplify only sequences present in multiple copies in theDNA sample Which of the following is a limitation on theuse of PCR to detect and isolate genes?
a. The sequence at the beginning and end of the DNA to be amplifiedmust be known
b. It also produces copies of sequences beyond the 5' and 3' end ofthe desired sequence
c. It cannot be used to amplify genomic DNA, only cloned DNA.
d. It will amplify only sequences present in multiple copies in theDNA sample

Explanation / Answer

Which of the following is a limitation on theuse of PCR to detect and isolate genes?
a. The sequence at the beginning and end of the DNA to beamplified must be known
    This is true - PCR works using 'primers', whichare complementary to the DNA sequence being amplified. If eitherthe 5' or 3' sequence is not known then we don't have the requiredforward and reverse primers, resulting in the DNA polymerase notknowing when to start or stop, depending on which one is missing.(Unless the DNA fragment is circular, in which case only one primeris needed.)
b. It also produces copies of sequences beyond the 5' and 3' end ofthe desired sequence
    Not true - once the DNA polymerase (taqpolymerase) reaches the end of the sequence it stops copying theDNA.
c. It cannot be used to amplify genomic DNA, only cloned DNA.
    Not true - PCR can be used to amplify both sortsof DNA provided both primers are known.
d. It will amplify only sequences present in multiple copies in theDNA sample
    Not true - if multiple copies of the sequenceare present in the sample then PCR will amplify all of the copies.However, it will still amplify the sequence even if there is onlyone copy of it.

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