HOW ACCURATE IS SIBLING DNA TESTing?

DNA Testing with Siblings: Accuracy and Guidelines

Sibling DNA Tests can indeed help determine biological relationships when a potential parent is unavailable. While generally reliable, it’s important to understand that sibling tests are not as conclusive as direct parent-child testing.

Including the mother’s DNA significantly improves the accuracy of a sibling test by allowing for the elimination of maternal genetic markers.

• Full siblings typically share approximately 50% of their DNA (with a range of about 38-61%),
• while half-siblings share an average of 25%.
• The results of a sibling DNA test are usually expressed as probability ratios or likelihood percentages, representing the statistical chance of a biological relationship.

When evaluating a sibling test, an accredited laboratory will compare the genetic markers between the individuals. The more genetic markers that match in the expected pattern for siblings, the stronger the probability of a biological relationship. However, the overall accuracy of a sibling test can vary depending on several factors:

• Whether the test involves full siblings or half-siblings
• Whether the mother’s DNA is included
• The number of genetic markers analyzed
• The statistical analysis methods used to interpret the results

For legal tests all DNA samples submitted to the lab are tested and analyzed by a partner AABB (The Association for the Advancement of Biotherapies and Biology) accredited DNA laboratory. The acquisition of this accreditation ensures your results will be recognized by Family Courts, Immigration Agencies, and U.S. Embassies worldwide.

Do legal and Home DNA Sibling Tests have the same accuracy?

Yes, the DNA samples are analyzed using the same scientific methods for both legal and home sibling tests.

Legal Tests: Results can be used for any legal purpose.

Home Tests/Non-legal: Results cannot be used for legal purposes. Home Tests do not require an unbiased DNA sample collector to collect samples or the establishment of chain of custody.

Sibling DNA test without parents: Can It Be Done?

Yes, sibling DNA testing can be performed even without the parents. However, including the mother’s DNA, if available, is highly recommended as it significantly improves the accuracy of the results.

DNA Sample Accuracy:

Below is a list of common DNA samples used for analysis:

• Cheek swabs: Preferred method for sample collection.
• Blood samples: Equally accurate as cheek swabs but more invasive and painful.

Forensic Sample Options: (Typically used when standard samples are unavailable)

• 8–10 hair follicles with the root attached.
• Toothbrush samples (collected after 6–8 weeks of consistent use).
• Earwax (collected on Q-tips and placed in an envelope).
• Bone samples (femur bones are preferred).

The accuracy of forensic samples depends on the quality of the sample collected.

How to read a sibling DNA test?

To read a sibling DNA test, you look at two main numbers:

Combined Relationship Index (CRI): This number shows how likely it is that the two people are siblings compared to being unrelated. A very high CRI, such as the example provided, strongly supports that they are full siblings.

Probability of Relatedness (or Sibling Probability): This percentage tells you the chance that the two people are actually siblings based on the test. A result of 99.99% means it is almost certain they are full siblings.

In simple terms, a very high CRI and a probability close to 100% mean the test strongly support a full sibling relationship. For half-siblings, these numbers would typically be lower but still indicative of a relationship.

Description of Exclusion: Exclusion happens when the test results show that two people cannot be siblings. This occurs if the DNA markers tested do not match in the way expected for siblings. In such cases, the Combined Relationship Index would be very low, and the probability of relatedness would be close to 0%, meaning no sibling relationship is supported by the DNA evidence.

How long does it take to receive sibling DNA results?

The average turnaround time for sibling test results to be completed is 2 to 3 business days from the date the lab receives all genetic samples.

Expedited same-day results are available for an additional fee. For more information or to order a Home DNA Sibling Test kit online, please call Secure DNA Tests at 888-970-4211 to schedule an appointment or order a Home Sibling DNA test kit here.

Conclusion:

Sibling DNA testing provides a valuable tool for establishing biological relationships in the absence of a parent. Understanding the factors affecting accuracy, the possibility of testing without parents, appropriate sample collection, and how to interpret the results are key to utilizing this technology effectively.