11
$\begingroup$

Suppose I want to preserve myself so that I can be reproduced as best as possible, in future or be simulated in future. At the moment full human genome sequencing is a bit expensive.

One could get some of my hair or saliva, but what can I do with it to best preserve it?

Would it need to be put in a freezer?

How long would the DNA of the hair or saliva be preserved for in a regular kitchen freezer?

How long would the DNA be preserved if the hair or saliva was not in a freezer?

Are there any issues of contamination?

Also, once the full genome sequencing has been done, is that all the info that could be gleaned from it genetically? can the hair/saliva be thrown out, or might it be possible that future human genome sequencing could pull more info from the sample?

$\endgroup$
  • 4
    $\begingroup$ Best of the two would be hair, since the saliva contains enzymes that degrade DNA. DNA is fairly stable, and the hairs could be kept at room temperature for future use. The problem with home freezers is that they defrost once in a while to lower the condensing ice that forms around it. These cycles of freeze-thaw are rather bad for everything you would want to keep in a lab. This is why we have non-defrosting freezers in labs. $\endgroup$ – WilliamL Sep 19 '15 at 14:47
  • 1
    $\begingroup$ @WilliamL how long would hair last at room temp? And how long in a non-defrosting freezer? $\endgroup$ – barlop Sep 19 '15 at 14:50
  • $\begingroup$ @barlop they've sequenced DNA from hair hundreds of years old. $\endgroup$ – MattDMo Sep 19 '15 at 17:43
  • 4
    $\begingroup$ As @MattDMo said, DNA from hair can last for very long in ambient conditions. Let's just say it could last for very very ... very long in a non-defrosting freezer. It just seems overkill much. Put your hair in a plastic bag (ziplock style) and put them in a binder/scrapbook (it will get creepy if you start a collection of those...). $\endgroup$ – WilliamL Sep 19 '15 at 18:05
  • 8
    $\begingroup$ Your biological information and your experiences are two entirely different things. You could make a cell for cell, protein for protein, base pair for base pair replica of yourself and that organism would be different as it will experience things differently than you have. Even identical twins are individuals. You can fool yourself into thinking that clone will be you, but they won't be, no more than a child will be you. They will carry more of your genetic code than a child or grandchild, but nurture plays a role in the person you develop into. Embrace your mortality, enjoy the ride. $\endgroup$ – AMR Sep 19 '15 at 19:41
2
$\begingroup$

Full genome sequencing is only one of many experimental approaches. It's important in the field of genomics and useful in transcriptomics and proteomics.

It's best to extract DNA as soon as the sample has been removed from the living organism since all kinds of physiological processes start breaking down DNA in dead tissue. Kitchen refrigerators are not ideal for storing extracted DNA because they operate at about four degrees celsius. In the lab, minus eighty degree freezers are used. The lower the temperature, the better. Minus eighty degrees, however, is good enough.

Contamination is a big problem, so the more technical repeats you run, and the more biological repeats you have, the better your chances of getting reliable results. Biological repeats refer to, for example, taking three strands of your hair for analysis, while technical repeats refer to, for example, carrying out three PCR experiments on material from the same strand of hair. Once you've used tissue to extract DNA you don't keep remaining tissue because it gets contaminated during experimental preparation. That is why you may want to have biological repeats. It's also important to take precaution when removing the sample from the organism. This means wearing latex gloves and even using dilute ethanol to sterilize the sample before placing it in a sterile container. The problem is that ethanol can interfere with DNA extraction and be a contaminant itself. Balancing contamination prevention with quality results is important in the lab.

There are additional biological information such as DNA methylation events that occur intermittently on a genome and are inheritable. This information cannot be predicted from the sequence composition of your genome, but there are experiments meant for elucidating methylation patterns that can be carried out using uncontaminated biological samples (such as hair and saliva) stored in eppendorf tubes at minus eighty degrees celsius.

$\endgroup$
  • 3
    $\begingroup$ "Kitchen freezers are not ideal for storing extracted DNA because they operate at about four degrees celsius." That would be a kitchen refrigerator, as that is 4° above the freezing point for water. A kitchen freezer operates at -20°C. The issue with most consumer freezer's are that they have an automatic defrost cycle, so the temperature is not maintained constantly at -20°C, which can cause sample or reagent degradation. $\endgroup$ – AMR Nov 8 '15 at 11:57
  • 1
    $\begingroup$ @AMR - Now that is interesting... $\endgroup$ – AliceD Nov 8 '15 at 12:34
  • 2
    $\begingroup$ @AliceD What? You think I am only a Biology hack? I know my way around household appliances! ;-) $\endgroup$ – AMR Nov 8 '15 at 12:39
  • 2
    $\begingroup$ @AliceD, also, I am pretty sure that -20°C is a holdover from 0°F, which is ~-18°C... so as you metric wonks like your base 10 numbers, you went with -20°C, because what is -2°C amongst friends.... $\endgroup$ – AMR Nov 8 '15 at 12:46
  • 1
    $\begingroup$ @AliceD sorry, idiomatic usage. What is x, amongst friends, is an idiom for a trivial detail that can be ignored, though it can also be used as irony as well... but I will save you from that explanation. Fahrenheit was proposed in 1724, Celsius in the mid 1740s, and Kelvin in 1848, so Fahrenheit was first. But refrigerators were mainly developed in the US, and as we hold onto the Fahrenheit scale.... Interestingly, 0°F is the temperature of brine made of equal parts ice and salt (that is where the zero point baseline was defined). en.wikipedia.org/wiki/Fahrenheit $\endgroup$ – AMR Nov 8 '15 at 15:35
0
$\begingroup$

As a general rule, you'd want to keep the sample as cold and dry as possible. If a sample is wet, heat/thaw cycles can damage tissue integrity due to ice crystal formation.

In the future, a small hair sample would probably only be able to recreate a small part of who you were, because it excludes epigenetic factors (methylation can be different in different parts of the body) and the entire microbiome.

$\endgroup$
0
$\begingroup$

In addition to -20 freezer, keeping your sample in 100% ethanol will help preserve your sample.

Cold temperatures help, because the bases (ATGC) in DNA can be damaged (deaminated) and even knocked out (depurinated) leaving abasic sites (and once that is lost no information can be recovered) and the DNA strand can be broken up into shorter and shorter pieces.

How long will a DNA sample survive in -20 freezer without other protection? Years. Decades if you are lucky. But it will probably be years.

How long will DNA in sample survive not in a freezer? Depends on ambient temperature, humidity and and microbe activity. Anywhere from days to years,

Contamination is a huge huge problem. A saliva sample is going to be very very contaminated and is going to degrade fast. A hair sample would be okay. But there is a certain trick to pulling hair to getting the follicular cells. A biopsy, some nice human tissue is even better.

DNA extraction from the sample is destructive process. Once the extraction process is done, the sample is gone.

$\endgroup$

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.