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Edexcel A2 SNAB (Biology)~ DNA profile help please!

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    Hello,

    I'm doing the exam for Topic 5 and 6 next week but am a little confused about something.

    When making a DNA profile what is the process?

    I know it is PCR then gel electrophoresis but where do the restriction enzymes (mentioned bottom of p.75) come in? What order does it all take place?

    (Ref. p.75-79 SNAB A2 textbook)

    Thanks in advance.
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    You would use restriction enzymes first. These cut long DNA strands into smaller DNA fragments. These are then amplified via PCR. The gel electrophoresis gives bands, each of which containing these smaller fragments.

    Hope that helps :-D
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    (Original post by BeckyDay)
    Hello,

    I'm doing the exam for Topic 5 and 6 next week but am a little confused about something.

    When making a DNA profile what is the process?

    I know it is PCR then gel electrophoresis but where do the restriction enzymes (mentioned bottom of p.75) come in? What order does it all take place?

    (Ref. p.75-79 SNAB A2 textbook)

    Thanks in advance.
    Hey! I'm doing this next week as well...

    Restriction enzymes come in to cut the STR (Short Tandem Repeats) within the introns (non coding part of the DNA)...

    These STR's occur at the same place on the chromosomes, but the number of STRs vary between individuals.

    And the restriction enzymes create fragments of the STRs which is used in DNA profiling and gel electrophoresis steps...
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    (Original post by BeckyDay)
    Hello,

    I'm doing the exam for Topic 5 and 6 next week but am a little confused about something.

    When making a DNA profile what is the process?

    I know it is PCR then gel electrophoresis but where do the restriction enzymes (mentioned bottom of p.75) come in? What order does it all take place?
    Oh, and DNA profiling is the process of obtaining the DNA, creating the fragments, and multiplying these fragments using a PCR machine, seperating these fragments and visualising the fragments using the method of gel electrophoresis.... this is to compare a DNA with a suspects DNA... and this highlights the STRs of the suspects and the ones you are comparing it to...
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    (Original post by Pedus)
    Oh, and DNA profiling is the process of obtaining the DNA, creating the fragments, and multiplying these fragments using a PCR machine, seperating these fragments and visualising the fragments using the method of gel electrophoresis.... this is to compare a DNA with a suspects DNA... and this highlights the STRs of the suspects and the ones you are comparing it to...
    Right so the DNA is extracted etc., the STR fragments are cut using restriction enzymes, then placed in the PCR to be amplified before gel electrophoresis?

    In the diagram though on p.77 they've put the DNA sample into the PCR but I can't see any restriction enzymes anywhere. Can you just amplify it then or could you use PCR or restriction enzymes?

    (Sorry if I sound stupid, this has confused me all year)
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    (Original post by BeckyDay)
    Right so the DNA is extracted etc., the STR fragments are cut using restriction enzymes, then placed in the PCR to be amplified before gel electrophoresis?
    Yes! Gel electrophoresis is the final step, where you analyse the different fragments and see if the original DNA matches any of the suspects..

    http://www.biocrawler.com/w/images/a...rophoresis.png

    In the diagram though on p.77 they've put the DNA sample into the PCR but I can't see any restriction enzymes anywhere. Can you just amplify it then or could you use PCR or restriction enzymes?

    (Sorry if I sound stupid, this has confused me all year)
    There wouldn't be any restriction enzymes there because:

    a) Restriction enzymes are used to cut up the DNA fragments before amplying the DNA sample.

    b) In that diagram, it is showing you the cycle of PCR. This is the process of making a lot of copies of the DNA sample, so you wouldn't need restriction enzymes in this process..

    Hope that helps!
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    (Original post by Pedus)
    Hey! I'm doing this next week as well...

    Restriction enzymes come in to cut the STR (Short Tandem Repeats) within the introns (non coding part of the DNA)...

    These STR's occur at the same place on the chromosomes, but the number of STRs vary between individuals.

    And the restriction enzymes create fragments of the STRs which is used in DNA profiling and gel electrophoresis steps...
    Hey, is the STR sequence same in every human in the same chromosomes?

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