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So, I would like to ask, why don't we use just DNA hybridization instead of PCR primer amplification to diagnise some illness?

I know, when you have a really small amount of DNA from virus or cell you need to amplifie it, so you can do some hybridizations. But I cannot find out, why you need to amplifie it when you have like 10 ml of substance, where the amount of cells or viruses can be really high.

For instance, when you are trying to diagnose some chromosomal aberation you don't amplifie the DNA, so you do just hybridization, but when you are trying to detect coronavirus you use PCR, why?

I have all the information from Genetics by Eduard Kočárek (Scientina 2008) - so now you know the literature my question is based on.

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    $\begingroup$ Could you be more specific about what you mean by "hybridization", e.g. Southern blot? I can assure you that Southern blots are extremely slow and laborious compared to PCR (1-2 days vs. 1-2 hours), more of the time is hands-on work, the technique is more difficult, and Southerns generally involve radioisotopes, which are complex to work with. blog.addgene.org/…. $\endgroup$ Sep 27 at 22:28
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    $\begingroup$ I’m afraid you really need to do some more reading and then edit your question so that it addresses the use of PCR in the diagnosis a specific disease or disease agent. Without that we can’t answer sensibly, as different diseases are diagnosed in different ways. $\endgroup$
    – David
    Sep 27 at 23:00
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    $\begingroup$ To add to the other excellent comments, think about what exactly you mean by "diagnose some illness". For example, looking for a genomic chromosomal aberration is very different than trying to determine what bacterium is present. What factors might vary between different types of diagnoses? $\endgroup$
    – Armand
    Sep 28 at 3:29
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From comment.

Could you be more specific about what you mean by "hybridization", e.g. Southern blot? This is the old-fashioned technique that I believe is closest to what you mean. Slot blots are also possible but somewhat less interpretable.

Both are still used occasionally for various reasons but each is much, much more work than PCR. Southern blots specifically are extremely slow and laborious compared to PCR (1-2 days vs. 1-2 hours), more of the time is hands-on work, the technique is more difficult, and Southerns (also slot blots) generally involve radioisotopes, which are complex to work with.

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