DNA testing examines an individual’s unique genetic code to identify specific characteristics. These tests are widely used for various purposes, including determining biological relationships, tracing ancestry, and identifying genetic predispositions or conditions. While generally reliable, DNA tests can have inaccuracies, meaning a “wrong” result can sometimes occur due to several factors.
The Basics of DNA Testing
DNA testing begins with collecting a biological sample, such as a cheek swab, saliva, or blood. This sample contains cells from which DNA is then extracted in a laboratory. Once isolated, the DNA undergoes a process called amplification, which creates millions of copies of specific DNA segments to allow for detailed analysis.
Following amplification, scientists analyze particular genetic markers within the copied DNA. These markers, known as short tandem repeats (STRs), are highly variable regions of DNA that differ significantly between individuals. By examining multiple STR markers, a unique genetic profile is generated for an individual. This profile is then compared against other profiles, such as those from potential relatives or reference databases, to establish relationships or identify specific genetic traits.
Laboratory Errors and Quality Control
Errors can originate within the DNA testing laboratory. Human error, such as mislabeling samples or mistakes during data entry, can lead to incorrect results. If a sample is incorrectly labeled, the genetic profile might be attributed to the wrong person. Such mislabeling can occur at various stages, from initial sample receipt to final analysis.
Another concern is cross-contamination, where DNA from one sample mixes with another. This can happen if equipment is not thoroughly cleaned or if proper sterile techniques are not followed. Contamination is a particular risk when dealing with very small or degraded DNA samples, as even a tiny amount of foreign DNA can produce misleading amplification products. Reputable laboratories implement stringent quality control measures, including physical separation of pre- and post-amplification areas and regular checks, to minimize these risks.
Sample Issues and Interpretation Challenges
Problems can arise before a sample reaches the laboratory or during result interpretation. Insufficient quantity or poor quality of the collected DNA can lead to inconclusive results. DNA can degrade due to improper storage, transport, or exposure to environmental factors like heat or moisture, making it difficult to obtain a complete and accurate genetic profile.
Interpreting DNA test results presents its own set of challenges. In kinship testing, results are often expressed as statistical probabilities, such as a 99.9% likelihood of a relationship, rather than absolute certainties. Additionally, ancestry tests rely on comparing an individual’s DNA to reference databases, and the completeness and diversity of these databases can affect the accuracy of ethnic origin predictions, especially for less represented populations.
Rare Biological Factors
Rare biological phenomena can alter an individual’s DNA profile, leading to unexpected test results. Chimerism is a condition where an individual possesses cells from two or more distinct zygotes, meaning they have different sets of DNA. This can occur when fraternal twin embryos fuse. If a DNA test samples cells from one genetic line while other cells from a different genetic line are involved in a biological process being tested, discrepancies can arise.
Mosaicism is another rare condition where an individual has two or more genetically different cell lines that originate from a single zygote. This means that not all cells in the body carry the exact same genetic information, which could potentially affect results if the tested sample does not represent all cell lines. Additionally, spontaneous mutations, which are changes in the DNA sequence that occur after conception, can appear in an individual’s genetic profile and might lead to an apparent mismatch in paternity or kinship tests, even if a biological relationship exists.
Addressing Discrepant Results
If DNA test results appear unexpected, individuals can investigate further. The first action should be to contact the testing company directly to inquire about their quality control procedures and to clarify any ambiguities in the report. Many reputable companies have customer support teams that can explain the results in detail and address concerns. This initial contact can often resolve simple misunderstandings or indicate potential issues with the testing process.
Considering a retest, either with the same or a different accredited laboratory, is a sensible approach. A retest can help confirm or refute the initial findings, especially if questions about sample integrity or laboratory procedures remain. It is important to choose a laboratory that is accredited by recognized bodies, as this indicates adherence to high standards of practice and regular external audits. Seeking a second opinion from a genetic counselor or a legal professional specializing in DNA evidence can also provide valuable insights and guidance on interpreting complex or challenging results.