Ancient DNA limitations and solutions
Taking a sample from a fossil for ancient DNA preparation.
DNA preservation
It is suggested that, under the right conditions, DNA can be preserved for up to a million years. These conditions include:
- a very cold and stable temperature
- absence of water
However, ancient DNA does degrade over time and its preservation is dependent on many chance events. Many biological remains degrade and decompose without leaving any trace at all.
Specimens in collections often haven’t been sampled and preserved with genetic analysis in mind.
Quality and contamination issues
Even if ancient DNA is preserved in a specimen, it can be of low quality when compared to modern DNA samples:
- The ancient DNA may be present in very small quantities.
- The DNA strands may be fragmented or otherwise degraded.
If the DNA signal is weak the analyses are very sensitive to contamination from DNA originating from modern sources.
This occurred in the early days of ancient DNA research, when DNA was reported to have been analysed from dinosaurs and insects preserved in amber, a hundred million years old or more.
We now know that these results came from contaminating DNA on the specimen or from modern DNA introduced during the extraction stage.
Solving the contamination issue
The contamination issue has largely been solved by:
- performing all ancient DNA work in a separate facility, well away from laboratories where modern DNA is processed
- cleaning floor and work surfaces on a regular basis with harsh chemicals such as bleach and hydrochloric acid, to keep the facility free from contaminant DNA
- researchers wearing full laboratory suits with face masks to protect the most ancient specimens
What is ancient DNA?
Ancient DNA can be described as any DNA extracted from ancient biological specimens, such as archaeological bones, teeth or other tissue.
Ancient DNA can derive from a wide spectrum of sources, including:
- animal and plant remains
- ice and permafrost cores
- marine sediments