I really need some help! My final goal is to make high quality DNA that can be labeled and used as a probe for southern blot. To this end, I have been isolating PCR products from an agarose gel, followed by Qiagen's gel extraction kit. However, my DNA doesn't seem to be that good, as there is often a hard time in using this DNA to make a radioactive probe for southern blot. Thus, I thought an alternative way to make probe DNA would be to do the same PCR reaction, but do a PCR purification instead of a gel extraction. Are there any advantages or disadvantages to this approach?