Hair can indeed be used for DNA testing, a practice common in various fields. While it is possible to extract DNA from hair, the success and type of DNA obtained depend on which part of the hair is collected and its condition. This method offers a non-invasive alternative to other sample types, such as cheek swabs or blood, especially when those are unavailable.
Hair Structure and DNA Location
Hair is primarily composed of a protein called keratin. Each hair strand originates from a hair follicle embedded within the skin. The follicle contains cells rich in nuclear DNA.
When a hair is naturally shed or cut, it often lacks the follicle, meaning it may not contain sufficient nuclear DNA for typical testing. However, if a hair is plucked, the follicle is frequently removed along with the hair shaft. This attached follicle, appearing as a small, light-colored bulb at the root end, is a source of viable nuclear DNA. The hair shaft itself, the part extending beyond the scalp, primarily contains mitochondrial DNA, which is present throughout in numerous copies.
Nuclear DNA Versus Mitochondrial DNA from Hair
Nuclear DNA (nDNA) is inherited from both parents, providing a unique genetic blueprint for each individual, making it suitable for identifying individuals or establishing paternity. For example, in paternity testing, a lab compares the extracted nuclear DNA from an alleged father’s hair to a child’s DNA, looking for similarities.
In contrast, mitochondrial DNA (mtDNA) is inherited exclusively from the maternal line, meaning all individuals in the same maternal lineage will share the same mtDNA profile. While mtDNA is highly abundant and more resistant to degradation, its maternal inheritance pattern means it cannot distinguish between maternally related individuals. Therefore, while useful for establishing maternal lineage or identifying unknown remains, it offers less discriminatory power than nuclear DNA for individual identification.
Factors Affecting DNA Extraction Success
The success of DNA extraction from hair samples depends on several factors. The presence of the hair root or follicle is paramount. For accurate results, especially for individual identification or paternity tests, hairs must be plucked and include the follicle, as shed or cut hairs typically lack sufficient nuclear DNA. Laboratories generally recommend collecting 7-10 hairs with intact follicles to ensure enough viable DNA.
The condition of the hair also influences success. Hair that has been chemically treated, such as bleached or dyed, or exposed to harsh environmental conditions, can have degraded DNA, making extraction more challenging. Environmental contamination, such as dirt or chemicals, can also impact the quality of the DNA sample. Hair samples, however, possess notable stability and can retain their DNA information for years or even decades when stored appropriately.
Applications of Hair DNA Testing
DNA testing using hair samples is employed in various scenarios, particularly when other biological samples are unavailable. Forensic investigations frequently utilize hair DNA to identify individuals involved in crimes, as hair is commonly found at crime scenes and can link people to locations or other individuals.
Hair samples can also be used for paternity testing, provided the hair root containing nuclear DNA is present. While less common than cheek swab testing for ancestry, hair samples with intact roots can offer insights into genealogical research, especially for tracing maternal lines through mitochondrial DNA. Additionally, hair follicle DNA extraction is being explored as a less invasive alternative for germline testing in medical contexts.