Yes, a DNA test can be done with just the alleged father and the child. While including the mother’s DNA sample can be helpful, it is not always strictly necessary for a conclusive paternity result. Paternity testing fundamentally relies on comparing genetic markers between individuals to establish a biological relationship.
How Paternity Testing Works
Each person’s DNA serves as their unique genetic blueprint, inherited equally from both biological parents. Paternity tests analyze regions of DNA called Short Tandem Repeats (STRs).
These are short sequences that repeat multiple times, with the number of repetitions varying significantly between individuals. Laboratories compare STR alleles between the alleged father and the child. If a biological relationship exists, the child’s DNA profile should consistently show markers inherited from the alleged father. This comparison involves analyzing 15 to 20 or more STR markers for high accuracy.
Testing Without the Mother’s Sample
A paternity test can be conducted with samples only from the alleged father and the child. While the mother’s DNA sample is often preferred because it helps exclude her genetic contribution, making the father’s contribution clearer, laboratories can still achieve highly accurate results without it. In such cases, the lab focuses on identifying genetic markers in the child that must have come from the biological father.
Scientists compare the child’s genetic profile directly to the alleged father’s, looking for shared STR alleles at each tested marker. If the alleged father is the biological parent, the child will possess specific alleles that match those found in the alleged father’s DNA. Even without the mother’s sample, if enough genetic markers align, the statistical probability of paternity can still be very high, often exceeding 99%. Motherless paternity tests are virtually as accurate as those including the mother’s sample.
Understanding Paternity Test Results
Paternity test results present two main outcomes: exclusion or inclusion. An “exclusion” means the alleged father is not the biological father, leading to a 0% probability of paternity. This occurs when too many mismatches exist in the genetic markers between the alleged father and the child.
An “inclusion” indicates the alleged father is the biological father, usually expressed as a very high probability, such as 99.9% or higher. This high percentage signifies that the likelihood of another unrelated individual having the same genetic profile and being the father is astronomically low. The calculation for this probability relies on a “Combined Paternity Index” (CPI), a statistical measure derived from individual matches at each genetic marker. A CPI greater than 1000 indicates a probability of paternity over 99%. A 100% probability is not reported because it would theoretically require testing every male in the world with a similar genetic background, which is not feasible.
Types of Paternity Tests
Paternity tests are categorized by their intended use and the strictness of their sample collection. “Peace-of-mind” or informational tests are for personal knowledge and can be conducted at home using self-collected buccal (cheek) swabs. These swabs are non-invasive and collect DNA from cells lining the inside of the cheek. While accurate for personal information, results from peace-of-mind tests are not admissible in court due to unverified sample collection.
In contrast, “legal” or court-admissible paternity tests require a strict “chain of custody.” A neutral third party, such as a medical professional or trained collector, must officially collect the DNA samples. Identities are verified, and samples are meticulously documented and tracked from collection to laboratory analysis. This stringent process ensures sample integrity and authenticity, making results legally binding for matters such as child support, custody disputes, or inheritance claims.