The number of cycles required for amplification depends on the number of copies of template DNA present at the beginning of the reaction. But what is the ideal number of cycles. Also if more no of cycles are required to amplify a house keeping gene like actin mean that the quality of RNA used is not good?
It depends on what are you amplifying. For genomic DNA amplicons with a length of about 100-200 bp, 35 will be good.
I have obtained excellent results even with 28 cycles. However in general 35 cycles are considered ideal. Check with 35 cycles if your interest band appears well marked and without inespecific bands. If your band is well marked but with some inespecific you can reduce the cycles and try 30-32. If your band is poorly marked and without nonspecific band can try to increase the number of cycles, for example 40. But if the band is clearly and with inespecific band, the increase the number of cycles also increase inesspecific. In this case will be best to change the temperature.
I am working on one sort of difficult pcr about cloning. I applied 33 cycles and got more product yield, when I switched to 36 cycles, there were many unspecific bands showed up. I agree with Danielle. The cycle number depends on lots of factors.
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