In family law proceedings, a DNA test result is often the definitive ‘final’ word in a dispute. For legal practitioners, managing client expectations is central, requiring a clear understanding of the potential results. To avoid delays or challenges to evidence, it is essential to understand not just what the results say, but what they mean, so that confident legal advice can be provided and the case stays on track.
Understanding 99.99% probability
The most common challenge for a solicitor is explaining why a ‘positive’ result is reported as 99.99% or higher rather than 100%.
DNA testing involves a process called short tandem repeat (STR) analysis to examine specific genetic markers. A child inherits one marker from the mother and one from the father, which are analysed for comparison. However, science cannot prove with 100% certainty that no other person shares that exact profile. To report 100%, a laboratory would, in theory, need to test every other male in the world to rule them out as the potential father.
Instead, a probability of paternity is calculated. A result of 99.99% is considered the highest standard in proving parentage. This probability comes from the statistical analysis of each participant’s DNA, considering how common each donor’s genotypes are in the general population.
Reading the report
The wording of a DNA test report is deliberately precise to meet the standards of the Family Law Reform Act 1969:
- The ‘positive’ result (inclusion): To ensure the highest level of certainty, accredited laboratories such as NorthGene™ require a result of 99.99% to confirm paternity. In these cases, the report will state ‘the results are consistent with paternity’. For all legal and practical purposes, this confirms the biological relationship between the child and the potential father.
- The ‘negative’ result (exclusion): To exclude the potential father as the biological father, a mismatch of seven genetic markers is required. The result will read as less than 0.02% probability and will state ‘the results are inconsistent with paternity’.
Inconclusive results
There are some cases in which an inconclusive result may be received, although this is less common in paternity and maternity testing. A result may be deemed inconclusive if the probability of a biological relationship is between 0.02% and 99.98%. This means that the laboratory was unable to confidently draw a conclusion from the similarities between the samples tested and may be due to various reasons:
- Genetic mutations: Occasionally, a natural mutation can occur within a donor’s genome, meaning it no longer perfectly matches a specific marker. By testing 23 unique genes, NorthGene™ lowers the risk of an inconclusive result.
- Related potential fathers: If the potential fathers are related, such as brothers or father and son, their DNA profiles will be very similar. In these instances, NorthGene™ strongly recommends including the mother’s sample – by subtracting her DNA from the child’s profile, the paternal markers can be isolated and compared with a higher level of conclusiveness.
Complex relationships
Siblingship, avuncular (aunt or uncle to niece or nephew) and grandparentage tests are less conclusive than parent and child tests because less DNA is shared by the participants. However, this is not to say that results cannot be derived from the samples. NorthGene™ offers a wide range of DNA relationship testing services for extended family.
An inconclusive result does not mean testing has failed – it means the scientific threshold for certainty has not been met. In these cases, further testing may be appropriate, such as:
- Including additional participants (most commonly the mother).
- Testing alternative relatives where paternity testing is not possible.
Discussing these options promptly with the testing laboratory can help keep proceedings moving and avoid unnecessary delays.
To learn more about conclusive results, click here.
The role of solicitors
As a family law professional, your role is turning a technical document into a legal reality. This begins with ensuring that testing is correctly instructed for legal purposes, independently witnessed and supported by a robust chain of custody, so that results can be relied upon without challenge.
A solid understanding of how DNA results are reported enables solicitors to manage client expectations from the outset. Explaining probabilities, the possibility of inconclusive outcomes and the circumstances in which further testing may be required can significantly reduce client anxiety and avoid unexpected costs or procedural delay.
Solicitors should also be aware of the practical considerations, including expected turnaround times and the steps that follow receipt of results. This allows hearings, negotiations and dispute resolution to be planned with greater certainty and efficiency. At NorthGene™, the organisation’s dedicated team is committed to delivering results within one to two working days of sample receipt at the laboratory.
Delivering legal clarity
DNA evidence often brings emotionally charged disputes to a decisive point. By understanding how DNA results are calculated, reported and interpreted, legal practitioners can give clear, confident advice, minimise challenges and help families reach resolution with clarity and finality.
To learn more about legal DNA testing with NorthGene™, visit the organisation’s website.
