Alternative High DNA-Yielding Bone Types for Aged Skeletal Remains

Introduction to DNA Analysis of Skeletal Remains

The analysis of DNA from aged skeletal remains poses unique challenges due to degradation over time. The petrous bone is widely regarded as one of the most reliable sources for high DNA yield in ancient remains. However, its destructive sampling process, coupled with the fact that petrous bones are not always present, necessitates the exploration of alternative bones for DNA extraction. In this article, we review a study comparing the DNA yield and STR (short tandem repeat) typing success from various bones, including petrous bones, femurs, calcanei, and tali.

Understanding DNA Preservation in Petrous Bones

The petrous bone, located in the temporal region of the skull, is well-known for its density and its ability to preserve DNA better than other bones. Studies have demonstrated that its dense structure helps protect the DNA from environmental factors that typically degrade genetic material. The petrous bone contains the otic capsule, which houses auditory and vestibular receptors, and this area is particularly resistant to decay. However, because obtaining DNA from petrous bones is highly destructive and the bone is not always part of recovered skeletal remains, it is essential to find other sources for DNA analysis.

Exploring Alternative DNA-Yielding Bones: Calcanei, Tali, and Femurs

This study compared DNA yields from petrous bones to those from femurs, calcanei (heel bones), and tali (ankle bones) in aged skeletal remains. The bones were sourced from two archaeological sites in Slovenia: Črnomelj (13th–18th century) and Polje (16th–19th century). These bones were analyzed for DNA quantity, quality, and STR typing success.

The calcanei and tali are trabecular bones, meaning they have a spongy internal structure. Previous research suggests that trabecular bones, such as those found in the foot, may be more suitable for DNA extraction than compact bones in some cases. The femur, a long compact bone, is frequently used in forensic investigations due to its durability and density, which aid in DNA preservation.

Comparative Study: DNA Preservation Across Different Bone Types

Key Findings from the Črnomelj Archaeological Site

• Petrous Bone: As expected, the petrous bone yielded the highest amount of DNA among the tested bones, exhibiting excellent STR typing success. Its ability to preserve DNA was superior in this older burial site.
• Calcaneus: The calcaneus also showed significant DNA preservation, with STR typing success comparable to that of the petrous bone. This finding suggests that the calcaneus can be an alternative for DNA analysis in older remains when the petrous bone is unavailable.
• Femur and Talus: The femur and talus exhibited lower DNA yields and STR typing success compared to the petrous bone. However, the calcaneus performed better than these bones in terms of DNA preservation.

Key Findings from the Polje Archaeological Site

• Petrous Bone: Once again, the petrous bone proved to be a high DNA-yielding bone, but the difference in DNA yield between the petrous bone and other bones was less pronounced at this more recent site.
• Calcaneus, Talus, and Femur: At this site, all three bones (calcaneus, talus, and femur) yielded similar STR typing success to that of the petrous bone. These findings suggest that in more recent burial sites, these trabecular bones, along with the femur, can serve as viable alternatives to the petrous bone for DNA analysis.

Factors Affecting DNA Preservation

DNA preservation is influenced by both intrinsic and extrinsic factors:

• Bone Density: Denser bones like the petrous bone tend to preserve DNA better than spongier bones like the talus and calcaneus, especially in older remains. However, trabecular bones may still yield significant DNA in more recent remains due to the preservation of soft tissues in the intertrabecular spaces.
• Environmental Factors: Burial conditions such as soil properties, humidity, UV exposure, and microbial presence significantly affect the preservation of skeletal remains and DNA.
• Post-Mortem Interval: The time elapsed since death plays a crucial role in DNA degradation. At the older Črnomelj site, trabecular bones were more degraded, whereas at the Polje site, trabecular bones preserved DNA more effectively due to the shorter post-mortem interval.

Practical Implications for Forensic and Archaeological DNA Analysis

The results of this study underscore the importance of careful sample selection when conducting DNA analysis on aged skeletal remains. While the petrous bone remains the gold standard for high DNA yields, other bones such as the calcaneus, talus, and femur can serve as viable alternatives depending on the burial site’s age and environmental conditions.

Recommendations for Forensic and Archaeological Investigations:

• Older Burial Sites: In older sites, calcanei may offer a viable alternative to the petrous bone for DNA extraction, especially when the latter is not available or its destructive sampling must be avoided.
• Recent Burial Sites: In more recent burial sites, femurs, calcanei, and tali can provide reliable DNA yields and STR typing success similar to that of the petrous bone. These bones also offer practical advantages such as easier sampling and grinding.

Conclusion

The preservation of DNA in aged skeletal remains depends on multiple factors, including bone density, environmental conditions, and the post-mortem interval. While the petrous bone consistently outperforms other bones in DNA yield, trabecular bones like the calcaneus and talus, as well as the femur, offer promising alternatives for DNA extraction, particularly in more recent remains. This study highlights the importance of selecting the appropriate bone type for DNA analysis, allowing for more efficient and effective forensic and archaeological investigations.