A paternity test compares the DNA of a child and an alleged father to determine a biological relationship. This process relies on the principle that a child inherits half of their genetic material from each parent. The test compares specific genetic markers to establish if the alleged father contributed the necessary genetic material. While modern paternity testing is highly accurate, often exceeding 99.9% for inclusion, results can still be incorrect. Errors are rare and typically stem from procedural lapses rather than flaws in the underlying science.
Understanding Test Reliability
The high reliability of paternity tests stems from examining specific, highly variable DNA regions called Short Tandem Repeats (STRs). STRs are short, repeating sequences that vary greatly in length among individuals, acting like a genetic fingerprint. Modern testing analyzes multiple STR locations, often 15 to 21 or more, to build a unique genetic profile for each person.
The laboratory compares the child’s STR pattern with the alleged father’s pattern, accounting for the mother’s contribution. This comparison generates a statistical measure called the Probability of Paternity (POP). For inclusion as the biological father, the POP must typically meet a threshold of 99.9% or higher, indicating it is statistically improbable for another randomly chosen man to match the child’s profile.
Errors Due to Sample Handling
The most frequent source of inaccurate results comes not from the DNA analysis itself but from procedural errors that occur before the sample reaches the analytical instruments. One common issue is the mislabeling of samples, where the DNA collection tubes or the accompanying paperwork are swapped between participants. This human error can lead to a result that accurately reflects the DNA profiles in the tubes but incorrectly assigns paternity to the wrong individuals.
Another risk is sample contamination, which occurs when foreign DNA or substances interfere with the collected material. This contamination can come from touching the collection swab tip, mixing with food or drink residue, or cross-contamination from multiple people handling the sample without proper precautions. If the DNA is mixed with another person’s cells, or if improper storage degrades the DNA quality, the laboratory may be unable to obtain a clear profile or may produce an inconclusive result.
Rare Biological Factors Affecting Accuracy
In extremely rare instances, biological factors within the tested individuals can complicate the results, even with perfect sample handling. One such factor is a spontaneous genetic mutation, which is a change in the child’s STR markers not inherited from either parent. A single mismatch at one STR locus is often attributed to this phenomenon, but if the lab does not use enough markers or fails to account for it, it can lead to a false exclusion.
More exotic conditions, such as chimerism, can also affect the outcome. Chimerism is a condition where a person possesses two distinct populations of DNA in their body, usually the result of absorbing a twin fetus in utero. If the DNA collected for the test comes from a cell line that does not match the one that formed the reproductive cells, the test could incorrectly exclude the biological father. While labs are equipped to detect these anomalies, they represent the biological limitations of the testing process.
The Importance of Chain of Custody
The distinction between a private, at-home paternity test and a legally admissible test rests entirely on the process of the Chain of Custody. Chain of Custody refers to a documented procedure that tracks the DNA sample from the moment of collection until the final analysis, ensuring its integrity and preventing tampering. This protocol minimizes the procedural errors that lead to inaccurate results.
For a test to be legally admissible, an impartial third party must collect and verify the samples, ensuring the identities of all participants through photo identification and documented consent. This validated collection process guarantees that the DNA analyzed truly belongs to the individuals named on the report. In contrast, while a private, non-legal test is scientifically just as accurate in the lab, the results can be challenged because the self-collected samples lack the verified documentation to prove they were not accidentally or intentionally swapped.