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Q28 - Ancient DNA Extraction

Theoretical 2 Real exam question - full text reproduced under IBO's CC BY-NC-SA 4.0 license
Biomolecular Analytical Techniques Nucleotide & Nucleic Acid Chemistry

Imagine you need to sequence DNA from a 25,000-year-old bone specimen.

DNA can be isolated using the following steps:

  1. Grind the bone into powder in liquid nitrogen.
  2. Add buffer with high salt concentration (high-salt buffer; HSB) to the powder and incubate.
  3. Add silica particles to the powder suspension and incubate.
  4. Remove the silica particles from the HSB and wash them with fresh HSB.
  5. Elute DNA from the silica particles using a buffer with low salt concentration.

This DNA isolation method is based on the ability of DNA to bind to silica particles in HSB as shown in the figure.

Nitrogenous base structures and principles of DNA purification on silica sorbent showing DNA binding at high salt and elution at low salt

True or False?

Q28.1. This DNA isolation method could also be used for modern samples.
Q28.2. This DNA isolation method allows scientists to obtain intact (full-length) chromosomes.
Q28.3. The DNA sample obtained with this method could be contaminated with bacterial DNA.
Q28.4. DNA binds to the silica particles via positively charged nitrogenous bases.
Q28.5. As some DNA bases undergo deamination when exposed to the environment, ancient DNA will contain more uracil compared to modern DNA of the same species.
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Question reproduced from IBO 2023, Theoretical Paper 2, licensed under CC BY-NC-SA 4.0 - attributed to the International Biology Olympiad. Open the full exam PDF