A DNA test examines an individual’s unique genetic code (DNA) to evaluate genetic conditions, establish biological relationships, or trace family heritage. A common question is whether hair can be used for these tests. Understanding hair as a DNA source involves exploring its composition and the requirements for successful DNA extraction.
Hair’s DNA Potential
Hair strands contain DNA, but its location and type are important for testing. Each hair consists of a shaft and a root, embedded in the skin within a follicle. The hair follicle is the primary source of nuclear DNA (nDNA), found in cell nuclei. Nuclear DNA is specific to an individual, inherited from both parents, making it ideal for paternity testing and forensic identification.
The hair shaft, the visible part, primarily contains mitochondrial DNA (mtDNA). This DNA is inherited solely from the mother and is less specific than nuclear DNA, as many individuals in the same maternal lineage share identical sequences. While advanced techniques can sometimes recover degraded nuclear DNA from rootless hair shafts, the follicle significantly increases the likelihood of obtaining a complete and usable nuclear DNA profile.
What Makes a Hair Sample Usable?
For a hair sample to be viable for DNA testing, it needs to include the hair follicle. This means hairs must be “pulled” from the scalp or body, not shed naturally or cut. The follicle, often a small white bulb at the hair’s base, contains the nucleated cells necessary for extracting nuclear DNA. Hairs without this attached root typically yield insufficient nuclear DNA for standard testing.
Laboratories usually recommend collecting five to ten hairs with intact roots to ensure enough genetic material. While some tests might succeed with fewer strands, providing sufficient quantity increases the chances of successful DNA extraction. Proper handling is also important; samples should be kept clean, dry, and handled minimally to avoid contamination or damage.
Challenges and Preferred Alternatives
Using hair for DNA testing presents several challenges affecting success rate and cost. DNA extraction from hair samples has a lower success rate (80-90%) compared to other sources. Hair samples are also susceptible to degradation from environmental factors like moisture, compromising DNA quality. Due to these complexities and specialized techniques, hair analysis can be more expensive.
Because of these limitations, other sample types are often preferred for DNA testing due to their reliability and ease of processing. Buccal swabs, collected by rubbing the inside of the cheek, are a common, non-invasive method yielding high-quality DNA. Blood samples are another reliable source, providing a high DNA yield, though their collection is more invasive. Saliva samples also offer a non-invasive, reliable method for DNA collection, suitable for many genetic analyses. These alternatives typically offer a more straightforward and consistently successful path to obtaining a DNA profile.
How to Collect Hair for Testing
If hair is the chosen sample type, careful collection is important for successful DNA extraction. Hairs must be pulled from the scalp or body, ensuring that the root or follicle is attached. Aim to collect approximately five to ten hairs with visible roots. Using clean tweezers can help in carefully plucking the hairs and minimizing contamination.
Once collected, it is important to handle the hairs as little as possible, particularly the root ends, to avoid transferring foreign DNA or oils. The samples should be kept dry, as moisture can degrade DNA, and stored in a clean paper envelope. Avoid using plastic bags for long-term storage, as they can trap moisture and promote degradation. Each sample should be clearly labeled with the donor’s name and the date of collection to prevent mix-ups. Storing hair samples in a refrigerator or freezer is not recommended, as it can lead to contamination or damage.