DNA and bone structure preservation in medieval human skeletons

Kinship analysis of 5th- to 6th-century skeletons of Romanized indigenous people from the Bled-Pristava archaeological site

The familial relationship between skeletons buried together in a shared grave is important for understanding the burial practices of past human populations. Four skeletons were excavated from the Late Antiquity part of the Bled-Pristava burial site in Slovenia, dated to the 5th to 6th century. They were anthropologically characterized as two adults (a middle-aged man and a young woman) and two non-adults (of unknown sex). Based on stratigraphy, the skeletons were considered to be buried simultaneously in one grave. Our aim was to determine whether the skeletons were related. Petrous bones and teeth were used for genetic analysis. Specific precautions were followed to prevent contamination of ancient DNA with contemporary DNA, and an elimination database was established. Bone powder was obtained using a MillMix tissue homogenizer. Prior to extracting the DNA using Biorobot EZ1, 0.5 g of powder was decalcified. The PowerQuant System was used for quantification, various autosomal kits for autosomal short tandem repeat (STR) typing, and the PowerPlex Y23 kit for Y-STR typing. All analyses were performed in duplicate. Up to 28 ng DNA/g of powder was extracted from the samples analyzed. Almost full autosomal STR profiles obtained from all four skeletons and almost full Y-STR haplotypes obtained from two male skeletons were compared, and the possibility of a familial relationship was evaluated. No amplification was obtained in the negative controls, and no match was found in the elimination database. Autosomal STR statistical calculations confirmed that the adult male was the father of two non-adult individuals and one young adult individual from the grave. The relationship between the males (father and son) was additionally confirmed by an identical Y-STR haplotype that belonged to the E1b1b haplogroup, and a combined likelihood ratio for autosomal and Y-STRs was calculated. Kinship analysis confirmed with high confidence (kinship probability greater than 99.9% was calculated for all three children) that all four skeletons belonged to the same family (a father, two daughters, and a son). Through genetic analysis, the burial of members of the same family in a shared grave was confirmed as a burial practice of the population living in the Bled area in Late Antiquity.

Freeze-drying improves DNA yield from teeth

The common method of preparing teeth prior to DNA extraction involves cleaning, decontamination, drying and pulverisation. Moisture in post-mortem teeth can promote bacterial growth and hydrolytic damage that could contribute to DNA degradation, whilst also possibly reducing the efficiency of sample pulverisation and DNA release. Here we compared DNA extraction from pig teeth, with- and without freeze-drying, to examine the impact of removing moisture on DNA yield. Quantitative real-time polymerase chain reaction (qPCR) was used to quantify an 83 bp mitochondrial DNA fragment and two nuclear DNA fragments of 82 bp and 150 bp. The comparative results showed that sample preparation with freeze-drying resulted in a higher DNA yield without compromising the DNA quality. This study highlights the advantage of incorporating a freeze-drying to improve the DNA yield and minimising the loss of DNA during sample preparation of teeth.

A systematic investigation of human DNA preservation in medieval skeletons

Ancient DNA (aDNA) analyses necessitate the destructive sampling of archaeological material. Currently, the cochlea, part of the osseous inner ear located inside the petrous pyramid, is the most sought after skeletal element for molecular analyses of ancient humans as it has been shown to yield high amounts of endogenous DNA. However, destructive sampling of the petrous pyramid may not always be possible, particularly in cases where preservation of skeletal morphology is of top priority. To investigate alternatives, we present a survey of human aDNA preservation for each of ten skeletal elements in a skeletal collection from Medieval Germany. Through comparison of human DNA content and quality we confirm best performance of the petrous pyramid and identify seven additional sampling locations across four skeletal elements that yield adequate aDNA for most applications in human palaeogenetics. Our study provides a better perspective on DNA preservation across the human skeleton and takes a further step toward the more responsible use of ancient materials in human aDNA studies.

A Simple and Efficient Method of Extracting DNA from Aged Bones and Teeth

DNA is often difficult to extract from old bones and teeth due to low levels of DNA and high levels of degradation. This study established a simple yet efficient method for extracting DNA from 20 aged bones and teeth (approximately 60 years old). Based on the concentration and STR typing results, the new method of DNA extraction (OM) developed in this study was compared with the PrepFiler™ BTA Forensic DNA Extraction Kit (BM). The total amount of DNA extracted using the OM method was not significantly different from that extracted using the commercial kit (p > 0.05). However, the number of STR loci detected was significantly higher in the samples processed using the OM method than using the BM method (p < 0.05). This study aimed to establish a DNA extraction method for aged bones and teeth to improve the detection rate of STR typing and reduce costs compared to the BM technique.