Analysis of Human Degraded DNA in Forensic Genetics

Abstract

Upon an organism’s death, enzymatic DNA repair ceases, exposing the genome to destructive factors such as free cellular nucleases and proliferating microorganisms, which can cause DNA loss. DNA preservation is highly dependent on environmental conditions, and less favorable environments accelerate degradation. Despite this, advanced extraction and analytical methods now enable the study of poorly preserved and degraded DNA. DNA typing is a foundation of forensic genomics, enabling the identification of individuals and the individualization of biological evidence through the generation of unique genetic profiles. Although DNA is relatively stable, environmental exposure initiates its degradation into progressively shorter fragments, complicating analysis. The extent of DNA preservation in biological evidence depends on numerous factors, and this review focuses on the environmental factors—including temperature, humidity, ultraviolet radiation, pH, chemical agents, and microbial activity—as the most influential variables. In samples with degraded DNA, the maximum amplicon length achievable through polymerase chain reaction (PCR) is inherently limited. This review discusses genetic markers and analytical strategies improvements that enable the examination of highly degraded samples, particularly when conventional short tandem repeat (STR) typing fails. In these situations, successful identification requires targeting short DNA fragments, which are more likely to persist. Single-nucleotide polymorphisms (SNPs) are a valuable alternative, as their high allelic variability and short amplicon requirements make them more amenable to amplification from fragmented templates than STRs. Advances in next-generation sequencing (NGS) technologies have further enhanced this capacity by enabling high-resolution SNP profiling, thereby improving outcomes in challenging forensic cases.