Svante Pääbo's study examines ancient DNA extracted from remains of various species, including two extinct animals, ranging in age from 4 to 13,000 years. The DNA was found to be of low molecular size and damaged by oxidative processes, leading to modifications of pyrimidines and sugar residues, as well as baseless sites and intermolecular cross-links. This damage makes molecular cloning difficult, but the polymerase chain reaction (PCR) can amplify and study short mitochondrial DNA sequences, offering insights into molecular evolutionary genetics. DNA from ancient remains has been extracted in several cases, but postmortem damage in DNA extracted from archaeological specimens poses challenges for molecular biological techniques. To assess DNA preservation, Pääbo extracted nucleic acids from 12 specimens representing diverse regions and time periods. The chemical modifications in these DNA samples make molecular cloning difficult, but PCR can produce reliable sequence information from many ancient tissue remains. DNA extraction involved a modified Blin and Stafford procedure, followed by ethanol precipitation and sucrose gradient centrifugation. Agarose gel electrophoresis, nick-translation of Alu repeats, end-labeling, and hybridization were used to analyze the DNA. Hydrolysis of DNA and HPLC of the bases were performed to assess damage. Ethidium bromide dot assays and gel staining were used to quantify ancient DNA, though concentrations were difficult to determine due to unknown components affecting dye intercalation. DNA damage was analyzed using hydrolysis and HPLC, revealing reduced amounts of cytosine and thymine, and the presence of new peaks indicative of ring-fragmented and/or ring-saturated pyrimidine derivatives. Alkali sensitivity tests showed that ancient DNA was highly sensitive to alkali, suggesting the presence of AP sites and modified sugar residues. Electron microscopy revealed that most DNA molecules were double-stranded and relatively small, with some cross-links and complex structures. Molecular cloning was attempted on DNA from a 4000-year-old Egyptian liver, but cloning efficiency was low due to damaged DNA. However, PCR was used to amplify mitochondrial DNA sequences, which are suitable for anthropological studies. PCR successfully amplified short mitochondrial DNA sequences, even from damaged DNA, showing that the size reduction and oxidative damage limit the size of amplifiable fragments. The study highlights the challenges of working with ancient DNA, including postmortem damage and contamination, but also demonstrates the potential of PCR to study ancient DNA for evolutionary and anthropological research. The results suggest that PCR can provide reliable sequence information from ancient tissue remains, opening new possibilities for studying historical, evolutionary, and taxonomic questions.Svante Pääbo's study examines ancient DNA extracted from remains of various species, including two extinct animals, ranging in age from 4 to 13,000 years. The DNA was found to be of low molecular size and damaged by oxidative processes, leading to modifications of pyrimidines and sugar residues, as well as baseless sites and intermolecular cross-links. This damage makes molecular cloning difficult, but the polymerase chain reaction (PCR) can amplify and study short mitochondrial DNA sequences, offering insights into molecular evolutionary genetics. DNA from ancient remains has been extracted in several cases, but postmortem damage in DNA extracted from archaeological specimens poses challenges for molecular biological techniques. To assess DNA preservation, Pääbo extracted nucleic acids from 12 specimens representing diverse regions and time periods. The chemical modifications in these DNA samples make molecular cloning difficult, but PCR can produce reliable sequence information from many ancient tissue remains. DNA extraction involved a modified Blin and Stafford procedure, followed by ethanol precipitation and sucrose gradient centrifugation. Agarose gel electrophoresis, nick-translation of Alu repeats, end-labeling, and hybridization were used to analyze the DNA. Hydrolysis of DNA and HPLC of the bases were performed to assess damage. Ethidium bromide dot assays and gel staining were used to quantify ancient DNA, though concentrations were difficult to determine due to unknown components affecting dye intercalation. DNA damage was analyzed using hydrolysis and HPLC, revealing reduced amounts of cytosine and thymine, and the presence of new peaks indicative of ring-fragmented and/or ring-saturated pyrimidine derivatives. Alkali sensitivity tests showed that ancient DNA was highly sensitive to alkali, suggesting the presence of AP sites and modified sugar residues. Electron microscopy revealed that most DNA molecules were double-stranded and relatively small, with some cross-links and complex structures. Molecular cloning was attempted on DNA from a 4000-year-old Egyptian liver, but cloning efficiency was low due to damaged DNA. However, PCR was used to amplify mitochondrial DNA sequences, which are suitable for anthropological studies. PCR successfully amplified short mitochondrial DNA sequences, even from damaged DNA, showing that the size reduction and oxidative damage limit the size of amplifiable fragments. The study highlights the challenges of working with ancient DNA, including postmortem damage and contamination, but also demonstrates the potential of PCR to study ancient DNA for evolutionary and anthropological research. The results suggest that PCR can provide reliable sequence information from ancient tissue remains, opening new possibilities for studying historical, evolutionary, and taxonomic questions.