Quick Answer
Yes, it is possible to extract DNA from hair that has been cut. As long as the hair follicle is still attached, DNA can be obtained. The follicles contain nuclei with DNA.
How Does DNA Extraction from Hair Work?
DNA extraction from hair involves obtaining the hair follicles which contain nuclei with DNA. Cut hair without follicles attached does not contain nuclei and will not yield DNA.
The steps for DNA extraction from hair are:
- Identify hairs with follicles attached and collect approximately 10-20 hairs.
- Clean the hair shaft to remove any external contaminants.
- Cut the hair 1-2 mm below the follicle using a scalpel.
- Place follicle(s) in a microcentrifuge tube and add lysis buffer to break open cells.
- Add proteinase K to digest proteins that protect the DNA.
- Incubate at 56°C for several hours.
- Optional: Add RNase to remove contaminating RNA.
- Precipitate DNA out of solution using alcohol.
- Wash DNA pellet with ethanol.
- Re-suspend DNA pellet in buffer or water.
The resulting DNA can be used for applications such as PCR amplification and DNA profiling. Approximately 1-12 ng of DNA can be obtained from a single hair follicle.
What Parts of the Hair Contain DNA?
Only the hair follicle contains nuclear DNA. The hair follicle is the portion of the hair embedded in the skin. It contains the hair root, which has layers of inner and outer root sheaths with nuclei. The area with the highest amount of DNA is the hair bulb, located at the base of the follicle.
The hair shaft does not contain nuclei or DNA. The shaft is composed of dead keratinized cells that lack nuclear DNA. Therefore, cut hairs without attached follicles will not yield DNA.
Factors Affecting DNA Yield from Hair
Several factors can affect the yield and quality of DNA extracted from hair:
- Hair color: Darker pigmented hairs tend to yield more DNA than lighter, grey, or white hairs.
- Hair type: Coarse, thick hairs with large follicles produce more DNA than fine, thin hairs.
- Storage conditions: Heat, humidity, and UV exposure degrades DNA over time if hairs are not stored properly.
- Chemical treatments: Dyes, bleaches, and perms can damage DNA.
- Pubic/axillary hair: Hairs from pubic and armpit regions tend to have higher DNA yields than scalp hair.
How Long Does DNA Last in Hair?
DNA can remain stable in the hair follicle for extended periods if stored appropriately. Hair is very resistant to degradation. Studies have shown successful DNA extraction from hair stored for over 30 years at room temperature. Hair found at crime scenes is often decades old but still contains usable DNA if the follicles are intact.
However, DNA does gradually degrade over time. Exposure to heat, humidity, sunlight, and chemicals will accelerate DNA degradation. For best results, hair samples should be stored in paper envelopes or bags in a cool, dark, dry location. Plastic containers can lead to more degradation.
Advantages of Using Hair for DNA Testing
There are several advantages to using hair as a source of DNA for forensic identification and ancestry testing:
- Non-invasive collection method
- Easy to transport and store
- Long-term stability of DNA
- Hairs shed frequently
- Single hair can provide sufficient DNA for profiling
- Does not require a living individual; can be collected from hairbrushes, clothing, etc.
Hair provides an abundant source of DNA that does not require blood draws or buccal swabs. Shed hairs can be recovered from items used by the person of interest and provide key evidence when other samples are not available.
Limitations of Hair DNA Testing
While hair is a useful DNA source, there are some limitations:
- No nuclear DNA in shaft, follicles required
- Shed hairs often lack follicles
- Low quantities of DNA compared to blood/saliva
- DNA degrades over time if stored improperly
- Chemical treatments damage DNA
- Environmental contamination can occur
- difficult to extract usable DNA from grey or white hairs
These challenges mean that hair DNA analysis works best with recent, untreated hairs with intact follicles. Multiple hairs may need to be tested. Care must be taken to avoid contamination from other sources. The use of appropriate collection and storage methods is critical.
Common Applications of Hair DNA Testing
Some common forensic, medical, and ancestral applications of hair DNA analysis include:
- Criminal investigations: Matching crime scene hairs to suspects.
- Missing persons: Identifying remains by matching hair to families.
- Genealogical research: Making connections based on shared DNA markers.
- Parentage testing: Verifying biological relationships.
- Monitoring drug use: Testing for substances ingested into the hair.
- Archeology research: Analyzing ancient hair DNA.
Hair provides a unique ability to acquire DNA non-intrusively for a wide array of purposes when other bio-fluids are unavailable.
Technical Considerations
There are some technical factors to consider when isolating DNA from hair:
DNA Extraction Methods
A variety of DNA extraction kits and methods can be used including silica-based column purification, magnetic bead separation, and phenol-chloroform extraction. The extraction method should isolate high molecular weight genomic DNA.
Quantification
Extracted DNA should be quantified by fluorescence or spectrophotometry to determine DNA yield and purity. Low yields may require concentrating samples or extracting additional hairs.
PCR Optimization
The PCR reaction may need optimization with extra cycles or additional template DNA to account for the low quantities from hair.
Quality Control
Proper controls should be used to detect contamination or PCR inhibitors. Replicate analyses provide confidence in results.
Data Analysis
Special interpretation is required due to risk of degradation and contamination. Results should be statistically evaluated to determine likelihood of matches.
Conclusion
Hair is a valuable source of DNA for forensic identification and ancestry testing purposes. As long as the hair follicle is present, nuclear DNA can be extracted and analyzed using various molecular biology techniques. With proper collection and storage methods, DNA in hair can remain stable for decades. While low yields and degradation can pose challenges, hair provides a non-invasive way to obtain reference DNA samples. When collected and handled correctly, the small amounts of DNA in hair follicles can yield powerful information.