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I am a high-school student learning about DNA fingerprinting. I know that satellite DNA is non-coding DNA and has a lot of repetitive sequences, and the length of each repeat can be either short or small.

The procedure of carrying out DNA fingerprinting I was reading about says that after doing gel electrophoresis, we hybridize the DNA fragments with VNTR probes and then we can identify the DNA.

My question is that how do I have the VNTR probe sequence ready from before?

What I thought is that all of us have the same SEQUENCE of the repeating DNA but the only thing that differs is the number of continuous repeats due to mutations. Am I thinking right?

So I am saying that me and the person reading this question have repetitive DNA with same sequence say (AGGTTCC) but the thing that differs is the number of continuous repeats. And in the lab, we have the radioactive probe (TCCAAGG) ready which we can hybridize and then check.

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  • $\begingroup$ I have tidied your question up a bit — having "question" in the title is clearly redundant on a Q&A site, and if you come onto a site for students and professionals of biology it's rude to "shout" that you are only a high-school student. However there were two points I couldn't deal with because they didn't make sense to me. What do you mean by "How do I have the VNTR probe sequence ready from before?" ? This isn't English and I honestly can't guess what it's supposed to mean. And what does continuous mean in "continuous repeats"? If they repeat they must be separate, not continuous. $\endgroup$
    – David
    Commented Apr 5 at 17:16
  • $\begingroup$ On this site you do not make statements like “if you don’t understand it’s not my problem”. They are considered unfriendly and condescending and I would normally flag to the moderators to remove them. However it IS your problem because you are the poster and your message is unclear to me, and being a molecular biologist of some standing I know that if I don’t understand you half the people reading this message will not. Try googling “continuous repeats”. You won’t find anything because it is not a term that is used. “Tandem repeat” is. $\endgroup$
    – David
    Commented Apr 9 at 11:37
  • $\begingroup$ Please refrain from using harsh language; our central theme here is 'be nice'; such language doesn't fit here and can result in a site ban. $\endgroup$
    – AliceD ♦
    Commented Apr 10 at 11:15

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Several things going on here. Briefly, yes, you are thinking right about what a VNTR is but there are several small points of clarification.

  • VNTRs are not satellites in the normal sense as they are quite short sequences and satellites are usually longer. Many such "microsatellite" or "short tandem repeat" (STR) sequences can be in genes and expressed into proteins.
  • The preferred method these days for fingerprinting would not be probing with radioactive probes (Southern blot) but rather PCR. PCR or similar lets you visually discriminate between alleles on a gel, and determine their lengths based on making many copies of a small DNA region. It works by leveraging the constant non-VNTR sequences immediately flanking the VNTR. It's much easier and less radioactive. See this illustrative figure from wikipedia:

STR genotyping schematic figure

  • You then don't need any such probe. PCR is much more quantitative than trying to hybridize a probe against the repeat unit and guess copy number. I am actually not sure how the probing approach that you suggest would work, you would probably instead probe a nearby non-repetitive sequence and see how different its size is on the gel (which would change based on VNTR copy number).
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  • $\begingroup$ Actually our syllabus only includes a very minimal portion of basics of DNA fingerprinting (just definitions of satellite DNA and probes and all), that's why I was trying to understand that, using PCR to do it is also interesting, anyway i just needed a basic understanding of its working and as you said i was thinking correctly, i am clear now $\endgroup$
    – Shivam Agarwal
    Commented Apr 4 at 16:47

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