KA RT-PCR Passage

[basophilic]

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What can serve as effective primers in reverse transcription PCR (assume all to be 8 nucleotides long)?
I Multitude of random, scrambled primers
III String of thymine nucleotides

Relevant background: RTPCR involves taking out mRNA from cell, reverse transcribing it to make cDNA, then amplifying that cDNA using regular DNA polymerase/PCR.

The answer included I and III.

I don't understand why choice III would be an answer. A primer (which I assume is ALWAYS made of RNA for any DNA polymerization...at least for PCR) should if anything have a poly-uracil chain to complement the poly-A tail of the mRNA.
Also, maybe choice I CAN work, but how is that even an EFFECTIVE method; for 8 nucleotides you'd need 4^8 different primers (and to prevent rehybridization, you'd need the usable primers to be far in excess to the material you're amplifying) - or is this done for UNKNOWN mRNA samples where you can't predict the primer?

 

[bee17]

I don't understand why choice III would be an answer. A primer (which I assume is ALWAYS made of RNA for any DNA polymerization...at least for PCR) should if anything have a poly-uracil chain to complement the poly-A tail of the mRNA.
Also, maybe choice I CAN work, but how is that even an EFFECTIVE method; for 8 nucleotides you'd need 4^8 different primers (and to prevent rehybridization, you'd need the usable primers to be far in excess to the material you're amplifying) - or is this done for UNKNOWN mRNA samples where you can't predict the primer?

This assumption is incorrect. Primers used in PCR are made of DNA.