Paternity testing is a scientific process used to determine the biological relationship between a potential father and a child. This analysis compares the genetic material of the individuals involved to provide a statistical probability of fatherhood. The testing establishes a definitive biological link, which can be sought for reasons ranging from personal knowledge to legal documentation. Utilizing advanced genetic technology, paternity testing offers highly accurate results.
How DNA Testing Works
Paternity testing operates by analyzing specific, highly variable regions of the human genome known as Short Tandem Repeats (STRs). STRs are short segments of DNA, typically two to six base pairs in length, that are repeated multiple times at a particular location, or locus, on a chromosome. The exact number of these repeats varies significantly between individuals, making them an excellent tool for relationship testing.
Every person inherits two copies of each chromosome, meaning they have two alleles at each STR locus: one from the biological mother and one from the biological father. During a paternity test, a laboratory analyzes a standard set of these STR markers in the child, the mother (if available), and the alleged father.
The test determines if one of the child’s alleles at every marker matches an allele from the alleged father, while the other allele is accounted for by the mother. If the tested man’s genetic markers align across all tested loci, it provides a genetic indication of a biological relationship. Analyzing a large number of these markers, often 20 or more, allows scientists to generate a highly unique genetic profile for comparison.
Types of Paternity Tests Available
The choice of paternity test is determined by whether the results are intended for personal knowledge or for use in a legal setting.
Informational Tests
Informational or private tests, often purchased as at-home kits, are designed for personal knowledge. These tests use the same laboratory analysis techniques as legal tests, but the results are not court-admissible because the sample collection process is not monitored.
Legal Tests
Legal paternity tests are required when the results must be presented as evidence in court for matters like child support, custody, or inheritance. To ensure the integrity of the results, these tests must adhere to a strict chain of custody, which includes having the sample collection witnessed by an impartial third party. Laboratories performing legal testing are typically accredited by organizations like the American Association of Blood Banks (AABB).
Non-Invasive Prenatal Paternity (NIPP) Testing
NIPP testing can be performed during pregnancy, often starting as early as seven or eight weeks gestation. This test requires a blood sample from the expectant mother, which contains trace amounts of the fetus’s cell-free DNA circulating in her bloodstream. The fetal DNA is isolated and compared to a cheek swab sample from the alleged father to determine paternity without posing any risk to the fetus or mother.
Collecting the Samples
The most common and least invasive method for collecting DNA samples is the buccal swab, often referred to as a cheek swab. This procedure involves gently rubbing a sterile swab against the inside of the cheek for 30 to 60 seconds. The goal is to collect buccal cells, which are the cheek lining cells that contain the DNA, rather than just saliva.
Before collection, individuals are instructed to avoid eating, drinking anything other than water, smoking, or chewing gum for at least an hour to prevent contamination or degradation of the sample. For informational, at-home tests, individuals collect their own samples, allow them to air dry, and seal them in provided paper envelopes. For a legal test, a trained and impartial collector verifies the identity of all participants, witnesses the swabbing process, and meticulously documents the transfer of the samples.
While cheek swabs are the standard, other biological samples can be used, especially for non-standard situations. These alternative samples, sometimes referred to as “forensic samples,” can include blood, hair with the root intact, or fingernail clippings. The viability of these samples depends on the laboratory’s ability to successfully extract a sufficient quantity of high-quality DNA for analysis.
Understanding the Test Results
The results of a paternity test are presented with one of two primary conclusions: inclusion or exclusion. An exclusion means the tested man is not the biological father, which is reported as a 0% probability of paternity. This conclusion is reached when a significant number of the child’s paternal alleles fail to match the alleged father’s alleles across the tested STR markers.
An inclusion, or “not excluded,” means the tested man is considered the biological father of the child. When a match is found across all tested genetic markers, the result is reported as a Probability of Paternity, typically 99.9% or higher. The report also includes a Combined Paternity Index (CPI), which represents the statistical odds of the tested man being the father compared to a random, untested man from the general population.
The probability of paternity is never reported as an absolute 100% because the calculation is statistical, based on population frequencies of the genetic markers. A 100% certainty would require testing every other male in the world, which is logistically impossible. Therefore, a result of 99.9% or higher is the scientific standard for concluding that the tested man is the biological father.