I would like to know the steps of this question and how to determine the forward and the reverse primers and also the length of the sequence, without using NCBI. If you could explain and give an answer step by step I would appreciate it. Thank youthe sequence is in the attached image

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    $\begingroup$ Wouldnt it be a question for chemistry or biology stack ? $\endgroup$
    – pippo1980
    Commented Oct 17, 2023 at 8:24
  • $\begingroup$ You are the second person to have raised this @pippo1980 exact point, Biology SE was suggested. If you flag this formally it helps to decide about migration. $\endgroup$
    – M__
    Commented Oct 17, 2023 at 13:38
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    $\begingroup$ I think it should be on SE Biology. Trying to flag with this. $\endgroup$ Commented Oct 18, 2023 at 18:10
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    $\begingroup$ This question tells me that you do not understand how PCR works. You should figure it out. Use Google search. $\endgroup$
    – Supertech
    Commented Oct 19, 2023 at 2:07
  • $\begingroup$ Just to note, the question has now received 2 closed requests. $\endgroup$
    – M__
    Commented Oct 24, 2023 at 14:20

1 Answer 1


Without giving too much of the "what they want you to do yourself" bits of this away, here are a few explanations of the image that may help you answer this question:

  • As mentioned in the text, the forward and reverse primers are underlined in the image.
  • The - and + symbols below the forward-direction sequence help determine the positions of the bases above and below. A + appears every 10 bases.
  • The first base in the sequence is at position 1441 (as indicated by the numbers) to the left of the sequence. The first + to the right of that first base represents position 1450.
  • Primers are usually represented as a sequence in a "5-prime to 3-prime direction", which is almost always the left to right direction of the top sequence in an image like this, and the right to left direction of the bottom sequence.
  • The length of a PCR product includes the primer sequence.

For help beyond that explanation... this looks like a canned question. Unless you give more context around what bioinformatics project you're working on and how this question relates to your project (i.e. explain why it's a real-world problem rather than a text-book question), I'm going to leave answers to the specific questions asked as an exercise to the reader.

  • $\begingroup$ So in this case what would be the length? $\endgroup$
    – Teo
    Commented Oct 17, 2023 at 6:19
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    $\begingroup$ I'm happy to help you understand the question, but I don't want to help you answer this question beyond that understanding. Other people are welcome to do that if they desire. $\endgroup$
    – gringer
    Commented Oct 17, 2023 at 10:06
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    $\begingroup$ @Teo you should be able to figure out the formula from what gringer has told you. We are not a homework writing service, our job is to help you understand so you can figure it out. So please read through what gringer has written, and see if you can figure it out. Then, if you still need help, update your question and add what you think the solution is and how you found it and then we can help you take it from there. If the information given here isn't enough for you, then update your question and add what you understand and what you feel is missing. $\endgroup$
    – terdon
    Commented Oct 17, 2023 at 12:01
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    $\begingroup$ @Teo Indeed there is a formula: b - a, where a is the start and b is the end point :) $\endgroup$
    – Cloudberry
    Commented Oct 17, 2023 at 18:32
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    $\begingroup$ @Teo if I start reading a book on page 20, and then close the book after page 30 and go have a cup of coffee, how many pages have I read? $\endgroup$ Commented Oct 18, 2023 at 18:17

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