Ancient DNA

Cross-linked DNA extracted from the 4,000-year-old liver of the ancient Egyptian priest Nekht-Ankh.

Ancient DNA (aDNA) is DNA isolated from ancient specimens. [1] [2] There is no definitive age to define historic or ancient DNA, but includes genetic material recovered from archaeological and historical skeletal material, mummified tissues, archival collections of non-frozen medical specimens, preserved plant remains, ice and permafrost cores as well as marine and lake sediments.

Due to degradation processes (including cross-linking, deamination and fragmentation) ancient DNA is of lower quality in comparison with modern genetic material [3]. The damage characteristics and ability of aDNA to survive through time restricts possible analyses and places an upper limit on the age of successful samples Allentoft et al. (2012). There is a theoretical relationship between time and DNA degradation [4], although differences in environmental conditions complicates things. Samples subjected to different conditions are unlikely to predictably align to a uniform age-degradation relationship [5]. The environmental effects may even matter after excavation, as DNA decay rates may increase [6], particularly under fluctuating storage conditions [7]. Even under the best preservation conditions, there is an upper boundary of 0.4-1.5 million years for a sample at around to contain sufficient DNA for contemporary sequencing technologies [8].

Research into the decay of mitochondrial and nuclear DNA in Moa bones has modelled mitochondrial DNA degradation to an average length of 1 base pair after 6,830,000 years at −5 °C. [9] The decay kinetics have been measured by accelerated aging experiments further displaying the strong influence of storage temperature and humidity on DNA decay. [10] Nuclear DNA degrades at least twice as fast as mtDNA. As such, early studies that reported recovery of much older DNA, for example from Cretaceous dinosaur remains, may have stemmed from contamination of the sample.

History of ancient DNA studies

The first study of what would come to be called aDNA was conducted in 1984, when Russ Higuchi and colleagues at the University of California, Berkeley reported that traces of DNA from a museum specimen of the Quagga not only remained in the specimen over 150 years after the death of the individual, but could be extracted and sequenced. [11] Over the next two years, through investigations into natural and artificially mummified specimens, Svante Pääbo confirmed that this phenomenon was not limited to relatively recent museum specimens but could apparently be replicated in a range of mummified human samples that dated as far back as several thousand years (Pääbo 1985a; Pääbo 1985b; Pääbo 1986). The laborious processes that were required at that time to sequence such DNA (through bacterial cloning) were an effective brake on the development of the field of ancient DNA (aDNA). However, with the development of the Polymerase Chain Reaction (PCR) in the late 1980s, the field began to progress rapidly. [12] [13]

Double primer PCR amplification of aDNA (jumping-PCR) can produce highly skewed and non-authentic sequence artifacts. Multiple primer, nested PCR strategy was used to overcome those shortcomings.

Single primer extension (abr. SPEX) amplification was introduced in 2007 to address postmortem DNA modification damage. [14]

Other Languages
català: ADN fòssil
Deutsch: ADNA
español: ADN antiguo
français: ADN fossile
italiano: DNA antico
polski: Antyczny DNA
português: DNA antigo
українська: Стародавня ДНК