Deoxyribonucleic acid, commonly known as DNA, is the fundamental blueprint containing genetic instructions for all known living organisms. This complex molecule is present in nearly every human cell, including blood, saliva, skin, and hair. DNA holds unique genetic information for each individual, which makes it widely used in medical diagnostics, ancestry tracing, and forensic investigations.
Sources of DNA on Fingernails
Fingernails are primarily composed of keratin, a tough protein also found in hair and skin. While the nail plate itself lacks intact DNA, the nail matrix at its base continuously produces DNA-containing cells. These cells undergo keratinization and programmed cell death as the nail grows. However, the most valuable sources of DNA associated with fingernails typically reside on or beneath the nail plate.
Skin cells are a common source of DNA found under fingernails. These can originate from the individual’s own skin, shedding from the nail bed or surrounding areas. During physical contact or struggle, skin cells from another individual can transfer and become trapped beneath the nails. Other biological materials like blood, saliva, or hair fragments may also accumulate under the nails, offering further DNA evidence.
Factors Affecting DNA Recovery
Successfully recovering usable DNA from fingernails presents several challenges. Contamination is a primary concern, as foreign DNA from dirt, nail polish, or environmental debris can mix with or obscure the target DNA. Cross-contamination may occur during sample collection or processing without proper protocols.
DNA degradation is another factor impacting recovery. Environmental elements like moisture, temperature fluctuations, and ultraviolet (UV) light can degrade DNA, making it more difficult to analyze. Older or previously handled nail samples may exhibit more degradation.
The quantity of DNA available from fingernails is often small compared to other biological samples like blood or saliva. While yields vary by extraction method, typical amounts range from 25 to 100 nanograms per milligram of nail. Collecting multiple nail clippings, usually 5 to 10, is recommended to obtain sufficient DNA for analysis. The specific collection method—clipping, swabbing, or scraping—also influences the amount and quality of DNA recovered.
Uses of Fingernail DNA
DNA recovered from fingernails holds significant value, particularly in forensic science. This evidence can identify individuals involved in an incident. By analyzing the unique genetic profile, forensic experts can link suspects to crime scenes or establish victim-perpetrator contact. This is particularly relevant in cases involving physical altercations where a victim may have scratched an assailant, leaving the attacker’s skin cells or blood under their nails.
Beyond criminal investigations, DNA from fingernails has other uses. It is a source for paternity and relationship testing when more common samples are unavailable. Fingernail DNA can also be used for post-mortem identification or ancestry testing. The ability to distinguish DNA from different individuals in mixed samples (e.g., victim and suspect) makes fingernail DNA a valuable tool for investigation and identification.