Paternity tests are a common method for establishing biological relationships, primarily fatherhood. While these tests are highly accurate, reaching probabilities of 99.9% or higher, understanding the science behind them and the rare factors that could influence results is important for interpreting results and addressing concerns.
The Science Behind Paternity Testing
Paternity testing relies on analyzing deoxyribonucleic acid (DNA), the genetic material passed from parents to offspring. Each individual inherits half of their DNA from their biological mother and the other half from their biological father. Scientists examine specific regions of DNA known as Short Tandem Repeats (STRs). These STRs are short, repeating sequences of DNA that vary in the number of repeats among individuals, useful for individual identification.
In a paternity test, DNA samples are collected from the child and the alleged father, often using cheek (buccal) swabs. Laboratories extract the DNA and use Polymerase Chain Reaction (PCR) to amplify the STR markers. By comparing the unique STR profiles, geneticists look for matching alleles, which are variations in the number of repeats at specific DNA markers. If the alleged father is the biological parent, their DNA profile should consistently match the paternal half of the child’s genetic markers.
Factors Influencing Paternity Test Accuracy
While DNA paternity tests are reliable, several rare factors can influence accuracy. Sample contamination or mix-up can occur during collection, handling, or laboratory processing. Eating, drinking, or smoking shortly before collecting a cheek swab can introduce foreign substances that compromise the DNA sample’s quality, potentially rendering it unusable. Cross-contamination can also happen if samples are collected or stored improperly, or if the swab tip is touched. However, reputable laboratories often detect such issues and may request new samples.
Rare genetic conditions can impact test results. For instance, chimerism is an extremely rare condition where an individual has two distinct sets of DNA, potentially leading to misleading results if the sampled tissue differs genetically from the reproductive tissue. Mosaicism, where some cells have a different genetic makeup, could similarly complicate analysis. Such biological phenomena are exceedingly uncommon and are typically investigated if unexpected results occur.
Testing related individuals, such as brothers of the alleged father, can complicate paternity results because close relatives share more DNA. In these situations, laboratories typically require DNA samples from all potential fathers to ensure accurate differentiation and avoid false inclusions. The number of genetic markers analyzed also plays a part; testing more markers generally increases the accuracy and reliability of the results.
Including the mother’s DNA sample in the testing process, while not always strictly mandatory, can significantly enhance accuracy and reliability. By comparing the child’s DNA to both parents, the laboratory can identify and exclude the mother’s genetic markers, allowing for a more precise analysis of the paternal contribution. This is particularly helpful in cases where a rare genetic mutation might have occurred in the child, as the mother’s sample can help confirm if a single mismatch is a mutation rather than an exclusion of paternity.
Interpreting Paternity Test Results
Paternity test reports typically present findings as a “probability of paternity” and a conclusion of “exclusion” or “inclusion.” The probability of paternity is expressed as a percentage, indicating the likelihood that the alleged father is the biological parent compared to a random individual. For an inclusion, this probability is very high, often reported as 99.9% or greater, signifying practical certainty. It is never 100% because it is a statistical calculation, and testing every male in the world with a similar genetic profile is not feasible.
Conversely, an “exclusion” means the tested man is not the biological father. In such cases, the probability of paternity is 0%, indicating a definitive lack of biological relationship. Laboratories often use a Combined Paternity Index (CPI) to calculate the probability of paternity, which reflects how many times more likely it is that the alleged father is the biological father than a random man.
Addressing Concerns About a Paternity Test Result
If you question a paternity test result’s validity, several actionable steps can be taken. First, contact the testing laboratory directly for clarification. They can explain the report in detail, review the testing process, and address any concerns about sample collection or analysis.
Considering a re-test is another option, potentially with a different accredited laboratory, especially if concerns persist. For legal purposes, ensure the test follows a strict “chain of custody,” which documents sample handling from collection to analysis, ensuring integrity and preventing tampering. Legal paternity tests require a neutral third party to collect samples.
Choosing a laboratory accredited by recognized bodies, such as the American Association of Blood Banks (AABB), Clinical Laboratory Improvement Amendments (CLIA), or the College of American Pathologists (CAP), provides assurance of adherence to high standards and rigorous protocols. If results have legal implications, such as for child support or custody, consult legal counsel. An attorney can guide you through challenging results in court and navigating legal aspects of paternity.