Revision Questions : DNA fingerprinting

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Question 1: Which of the following is/are the reason(s) of using VNTRs in DNA fingerprinting?
    1. The number of repetitive sequences at each VNTR locus shows polymorphism.
    2. The DNA at VNTR loci is more stable than coding DNA.
    3. The DNA sequence of each tandem repeat at a VNTR locus shows polymorphism.
  • CORRECT! Different number of repetitive sequences gives different lengths of DNA fragments after digestion by restriction enzyme, which allows one to generate a DNA fingerprint.
  • INCORRECT! There is no difference in the stability of DNA at coding or non-coding region.
  • INCORRECT! There is no difference in the stability of DNA at coding or non-coding region.
  • INCORRECT! There is no difference in the stability of DNA at coding or non-coding region. The number but not the DNA sequence of VNTRs shows polymorphism.
Question 2: Which of the following determines the rate of DNA migration across the agarose gel?
    1. Molecular size of the DNA
    2. Applied voltage
    3. Agarose gel concentration
    4. Length of agarose gel
    5. The net charge of DNA
  • CORRECT!
  • INCORRECT! In a buffer of standard pH, the net charge of all DNA in the agarose gel is negative and equal per unit length of DNA.
  • INCORRECT! The length of agarose gel only determines the time for electrophoresis but not the rate; In a buffer of standard pH, the net charge of all DNA in the agarose gel is negative and equal per unit length of DNA.
  • INCORRECT! The length of agarose gel only determines the time for electrophoresis but not the rate; In a buffer of standard pH, the net charge of all DNA in the agarose gel is negative and equal per unit length of DNA.
Question 3: Which of the following statement is CORRECT?
  • INCORRECT! The radioactive DNA probes bind on complementary nucleotide sequences on DNA samples.
  • INCORRECT! The DNA samples are transferred to the nylon membrane by capillary action
  • CORRECT! The DNA probes can bind with the DNA sample in agarose gel, but the efficiency is higher on nylon membrane.
  • INCORRECT! Alkali is used for such purpose.
Question 4: In gel electrophoresis, which of the following will happen if the TBE buffer solution is replaced by distilled water?
    1. DNA will not run through the gel
    2. DNA inside the gel will be easily degraded.
    3. DNA will carry positive charge.
  • INCORRECT! One more consequence will happen
  • INCORRECT! One more consequence will happen
  • CORRECT! TBE buffer provides ions for the electric current, which drives the movement of the DNA. It also maintains the pH and protects DNA from digesting by nucleases through chelating the Magnesium ions which are co-factors of nucleases
  • INCORRECT! DNA is still negatively charged in distilled water
Question 5: Referring to the following DNA fingerprint, what of the following statement is WRONG?
  • CORRECT! There is still chance, although very low, about 1/5 billion, another person may share the same DNA fingerprint, example: identical twins
  • INCORRECT! This statement is true
  • INCORRECT! This statement is true
  • INCORRECT! This statement is true