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Imagine a person in the early half of the 20th century (1900 to 1950) took some kind of sample(s) from a living human body using any technology of the era. They then stored it using any technology available, but could not use prolonged (70+ years) refrigeration.

We want to be able to do useful analysis of that sample in the year 2024. We particularly might want to be able to sequence mtDNA and nucleus DNA, look at telomeres and methylation. Furthermore, we especially want to be able to try to determine the age of the individual, and even better, from what approximate generation they were (i.e. plus/minus a hundred years).

Is such sample storage even possible?

Using my "just enough knowledge to ask stupid questions":

  • Could a sample be preserved in formalin and then immersed in alcohol, all in an air-free sealed container, and preserve the needed DNA strands and/or other biochemistry?
  • Could ethanol precipitation of DNA be used on the sample contemporaneously, and that precipitate instead be stored safely for 70+ years?

Maybe these other questions apply?

(I'm an old hand at Stack Overflow / Stack Exchange sites, but this is my first post to Biology. Gentle feedback appreciated.)

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2 Answers 2

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If you're wanting to store DNA long-term at room temperature, you'll probably want to dry it. DNA extraction methods have been known since 1869. You can then use ethanol to precipitate the DNA, centrifuge it, and dry off the ethanol. The dried DNA pellet is surprisingly stable (though still maybe not great at this time scale, depending on what you want to do with it). Adsorbing the DNA onto a matrix, including silk, can increase preservation.

You could also try preserving the tissue itself. Two good options would be freeze drying the tissue, or preserving it in 95% ethanol. You would not want to store in formalin, as that creates DNA fragmentation and cross-linkages.

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  • $\begingroup$ Thank you so much! That's exactly the kind of knowledge I was looking for! $\endgroup$
    – CXJ
    Commented Feb 24 at 2:23
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For anyone curious, @Darlingtonia's answer is what I needed. It also gave me the search terms that Google could use to finally find further useful information. In particular, a paper published at the National Center for Biotechnology Information, linked here.

https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3910151/

First paragraph of the abstract:

The globalization of DNA barcoding will require core analytical facilities to develop cost-effective, efficient protocols for the shipment and archival storage of DNA extracts and PCR products. We evaluated three dry-state DNA stabilization systems: commercial Biomatrica® DNAstable® plates, home-made trehalose and polyvinyl alcohol (PVA) plates on 96-well panels of insect DNA stored at 56 °C and at room temperature. Controls included unprotected samples that were stored dry at room temperature and at 56 °C, and diluted samples held at 4 °C and at −20 °C. PCR and selective sequencing were performed over a 4-year interval to test the condition of DNA extracts. Biomatrica® provided better protection of DNA at 56 °C and at room temperature than trehalose and PVA, especially for diluted samples.

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