When DNA Tests Lie: Understanding False Positives in Paternity Testing

Paternity tests are considered the definitive way to determine the biological father of a child. DNA testing is reliable and accurate and has been used in countless cases to establish paternity. 

However, like any other scientific method, there are instances where false results can occur. 

In this article, we will explore the causes of false positive DNA results on paternity tests and the steps you can take to prevent them.

Causes of False Positive DNA on Paternity Tests:

1. Contamination of The DNA Sample Can Cause a False Positive DNA Test

Contamination is one of the leading causes of false positive DNA results on paternity tests. This occurs when foreign DNA is introduced into the testing sample. 

The most common source of contamination is the swab used to collect the DNA sample. It is essential to use a sterile swab and ensure that it is not contaminated by any other substance. 

One notable case where contamination of DNA caused a false positive result is the case of Lukis Anderson, a homeless man who was falsely accused of murder

Anderson’s DNA was found on the victim’s clothing, leading to his arrest and detention. However, it was later revealed that Anderson’s DNA had been transferred to the clothing via a paramedic who had treated Anderson earlier that night. 

The paramedic had unknowingly transferred Anderson’s DNA to the victim’s clothing while treating the victim at the crime scene.

2. Mislabeling Can Cause a False Positive DNA Test

Mislabeling is another common cause of false positive DNA results on paternity tests. This occurs when the sample is incorrectly labeled or mixed up with another sample. 

This mistake can happen at any point during the testing process, from the sample collection to the analysis of the results. 

For example, in a paternity test, a mix-up or mislabeling of samples can lead to a false positive result, where a man is identified as the biological father of a child even though he is not. 

This can happen when samples are not properly identified, or there is a mix-up between samples from different individuals.

It is essential to ensure that the sample is labeled correctly and that the testing facility has a reliable system in place to prevent mislabeling.

3. Cross-Reactivity Can Cause a False Positive DNA Test

Cross-reactivity occurs when the DNA sample contains genetic markers similar to those found in another individual.

For instance, let’s say that a woman has a sexual relationship with two men who are closely related, such as a father and son. 

A paternity test may show that the son is the child’s biological father, even though it is actually the father who is the true biological father. 

This is because the son’s DNA is very similar to the father’s, leading to a false positive result.

4. Technical Errors Can Cause a False Positive DNA Test

Technical errors can occur during any step of the testing process, from the sample collection to the analysis of the results. 

For example, in a paternity test, technical errors can occur if there is a problem with the DNA extraction process, such as inadequate sample collection or improper storage of the sample. 

Technical errors can also occur during the amplification process, where mistakes in the PCR (polymerase chain reaction) technique used to amplify the DNA can lead to false positive results.

One high-profile case where technical errors caused a false positive DNA test result is the case of Lydell Grant. In 2012, Grant was arrested and charged with the murder of Aaron Scheerhoorn, a man stabbed to death outside a nightclub in Texas.

DNA evidence found at the crime scene was used to convict Grant of the murder, and he was sentenced to life in prison. However, in 2019, new DNA testing methods were used to reanalyze the evidence, and it was discovered that the DNA found at the scene did not match Grant’s DNA.

The technical error occurred because the original DNA testing methods used in 2012 were not sensitive enough to detect the small amounts of DNA at the crime scene. 

The new DNA testing methods used in 2019 were more advanced and able to detect the DNA of a different person who had been at the crime scene.

The discovery of the error led to Grant being released from prison after spending seven years behind bars for a crime he did not commit. 

The case highlighted the importance of using the most advanced and reliable forensic science techniques to ensure accurate DNA results.

These errors can result in false positive DNA results on paternity tests. Using a reputable testing facility with reliable equipment and experienced technicians is essential to minimize the risk of technical errors.

5. Human Error Can Cause a False Positive DNA Test

Human error is also a common cause of false positive DNA results on paternity tests. This can occur when the sample is mishandled, misinterpreted, or misreported. 

One example of a human error in DNA testing is the case of Joyce Gilchrist. Gilchrist was a forensic scientist who worked for the Oklahoma City Police Department for over 20 years and was involved in the analysis of DNA evidence in numerous criminal cases.

In the late 1990s, it was discovered that Gilchrist had made numerous errors and committed several instances of misconduct in her handling and analysis of DNA evidence. These errors included failing to conduct proper tests, misinterpreting results, and even falsifying evidence to secure convictions.

One notable case involved the conviction of Jeffrey Pierce for the murder of a 9-year-old girl. Gilchrist had testified that DNA evidence on the victim’s body matched Pierce’s DNA. 

However, it was later discovered that Gilchrist had misinterpreted the DNA results and that the evidence did not match Pierce’s DNA.

The human error, in this case, was attributed to Gilchrist’s lack of training, supervision, and oversight. She was allowed to operate largely unsupervised and without proper quality control measures, leading to numerous errors and misinterpretations of DNA evidence. 

It is essential to use a reputable testing facility with a rigorous quality control process to prevent human error.

What To Do If You Suspect a False Positive on Your Paternity DNA Test

If you suspect a false positive on a paternity DNA test, you should consider taking the following steps:

1. Verify That a Reputable Laboratory Did the Testing

Make sure that an accredited and reputable laboratory did the paternity DNA test to ensure the accuracy of the results.

2. Seek a Second Opinion

Consider seeking a second opinion from another DNA testing laboratory to verify the results. The second laboratory should use different genetic markers to test for paternity.

3. Confirm the Identity of the Tested Parties

Confirm the identity of the individuals who were tested, as mix-ups or errors in sample collection can lead to false positives.

4. Check for Technical Errors

In rare cases, technical errors can occur during DNA testing, leading to false positives. Speak with the laboratory that conducted the test to understand their testing procedures and see if there were any issues with sample collection, processing, or analysis that could have led to inaccurate results.

5. Get Legal Advice

If the paternity DNA test results could have legal implications, such as for child support or custody, you may want to seek legal advice from a family law attorney who can guide you through the legal process and provide additional options.

How Accurate Are DNA Paternity Tests? 

DNA tests for paternity are highly accurate and have a very low probability of producing false results. Most reputable laboratories claim an accuracy rate of 99.9% or higher for paternity testing. 

This level of accuracy is achieved through the analysis of genetic markers in the DNA of the tested parties. These markers are unique to each individual and are inherited from their biological parents. 

By comparing the markers in the DNA of the alleged father and the child, a paternity test can determine whether or not the alleged father is the child’s biological father.

It’s important to remember that a paternity test’s accuracy depends on the DNA sample’s quality and the number of genetic markers analyzed.

 A higher number of markers analyzed can increase the accuracy of the test. In addition, it’s crucial to have the testing done by a reputable laboratory to ensure accurate results.

Overall, DNA tests for paternity are considered highly accurate and reliable, with a very low chance of producing false results.

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Tim McDuffey is a practicing attorney in the State of Missouri. Tim is a licensed member of the Missouri Bar and Missouri Bar Association.

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