Paternity testing establishes a biological relationship between a potential father and a child by comparing their unique genetic markers. This process requires obtaining a high-quality DNA sample from all tested individuals. While hair contains genetic material, its viability for a definitive paternity test is highly conditional and presents significant challenges compared to preferred methods.
The Viability of Hair Samples
Using hair for a paternity test is technically possible, but it is rarely the preferred method due to strict requirements for sample integrity. The hair strand has two parts: the shaft (the visible, dead portion) and the root (the living part embedded beneath the skin). Only hair that has been forcibly removed and contains an intact root, or follicle, will contain the necessary biological material for a standard paternity test.
The hair shaft alone, typically found after natural shedding or cutting, is generally unusable for establishing paternity. Laboratories require five to ten hairs with complete roots attached to ensure they can extract a sufficient quantity of DNA. Collecting a high-quality sample with the root intact outside of a controlled, clinical environment is difficult. If the root is damaged, crushed, or absent, the sample is unlikely to yield a conclusive result.
Understanding DNA Requirements for Testing
The strict requirement for the hair root is due to the type of genetic material needed for accurate paternity determination. Paternity testing relies on the analysis of nuclear DNA, which is located within the cell nucleus and contains a complete set of genetic information inherited from both parents. This nuclear DNA is housed in nucleated cells, which are abundant in the hair root but largely absent in the hair shaft.
The hair shaft is primarily composed of keratinized, dead cells that lack a nucleus. While shafts may contain mitochondrial DNA (mtDNA), this genetic material is only inherited from the mother and is unsuitable for establishing paternity. Even if the root is present, the DNA is fragile and prone to degradation from environmental factors like heat or humidity. Extracting usable DNA from hair samples is often technically challenging and less reliable than from other sources.
Preferred Methods for Paternity Sample Collection
The preferred method for collecting a DNA sample for paternity testing is the buccal swab, which involves gently rubbing a sterile cotton swab inside the cheek. This non-invasive and painless procedure quickly collects cheek cells, which are rich in the nucleated cells necessary for obtaining a high-yield DNA sample. The ease of collection makes the buccal swab ideal for all ages, including infants and young children. Blood samples collected through venipuncture are also highly reliable, though less common for routine testing due to their invasive nature.
Both cheek swabs and blood samples provide genetic profiles with the same high degree of accuracy, which is typically greater than 99.9%. For testing used in legal contexts, the collection method must adhere to a strict chain of custody. This ensures the sample collector verifies the identity of the person being tested and maintains integrity from collection to arrival at the laboratory.
Non-invasive prenatal paternity testing, performed as early as seven weeks into a pregnancy, utilizes a blood sample from the mother and a cheek swab from the alleged father. The mother’s blood contains small amounts of cell-free fetal DNA, which a laboratory can separate and analyze. The simplicity and reliability of the buccal swab have made it the gold standard for postnatal testing.