Paternity testing uses deoxyribonucleic acid (DNA) analysis to determine the biological relationship between a presumed father and a child. Modern techniques offer a high degree of accuracy, making DNA analysis the most reliable method available for establishing parentage. Laboratories compare the unique genetic profiles of individuals. Understanding this process involves examining genetic inheritance, the specific laboratory techniques used, the meaning of the final report, and the practical steps of sample collection.
The Genetic Blueprint
Every person inherits exactly half of their genetic material from each biological parent. The child receives 23 chromosomes from the mother and 23 from the father, forming the child’s unique genetic code. For every location (locus) on the child’s DNA, one segment must match the mother and the other must match the father. Paternity testing focuses on specific, highly variable regions of the DNA known as genetic markers. By analyzing these sites, scientists determine if the child’s paternal genetic contribution could have come from the man being tested.
The Testing Process
The core of modern paternity testing analyzes Short Tandem Repeats (STRs), which are sequences of 2 to 6 base pairs repeated multiple times. The number of repeats varies greatly, making STRs highly effective for individual identification. Laboratories typically analyze 15 to 25 distinct STR markers to establish a genetic profile for each person tested.
Once DNA is extracted, the lab uses Polymerase Chain Reaction (PCR) to amplify the STR markers, making millions of copies of the specific DNA sections of interest. The amplified STR fragments are then measured to determine the exact number of repeats at each location, creating a unique numerical profile. The child’s paternal markers are compared against the alleged father’s profile, and a match at every tested locus is necessary for inclusion as the biological father.
Interpreting the Results
The final laboratory report provides two primary indicators: the Combined Paternity Index (CPI) and the Probability of Paternity (POP). The CPI is a ratio representing how many times more likely it is that the alleged father is the biological parent compared to a randomly selected male in the same population. This index is calculated by combining the ratios from all tested genetic markers.
The POP converts the CPI into a percentage. If the alleged father is not excluded, the result shows a probability of paternity of 99.9% or higher, the accepted standard for legal proof of parentage. If the genetic profiles do not match at two or more tested STR loci, the man is “excluded” as the biological father, and the POP is 0%.
Sample Collection and Test Types
The most common and least invasive method for collecting a DNA sample is the buccal swab, where a swab is gently rubbed on the inside of the cheek. This painless process collects cheek cells containing the necessary DNA. The accuracy of a cheek swab sample is equal to that of a blood sample, making it the industry standard for most post-natal tests.
Peace of Mind vs. Legal Testing
An important distinction exists between “Peace of Mind” and “Legal” testing, which share the same scientific process but differ in administrative requirements. Peace of Mind tests are for personal information only and can be done entirely at home. Legal tests, which are court-admissible, demand a strict “chain of custody” protocol. This requires a certified professional to collect the samples, verify the identity of all tested parties, and ensure the samples are sealed and documented.