Sibling Test – Full and Half


This type of DNA test determines the likelihood statistical probability that two or more persons are related as brothers and/or sisters. A sibling test is normally done when a paternity test is not an option and thus the only means of establishing paternity is by testing the alleged father’s suspected children to see whether they are related to each other.

In a sibling comparison, the two or more siblings that are being tested don’t have to share DNA in common at all the markers like a father and child. This means that the outcome of a sibling comparison relies solely on statistics.

When performing asibling case, we are trying to determine if it is more likely that they share two common parents, one common parent or no common parents. To put it another way, are the parties we are testing full siblingshalf siblings, or unrelated.

Unlike a DNA paternity test which will always provide a conclusive result, sibling DNA testing is different. When a sibling DNA test is conducted, the laboratory will determine the genetic profile of the alleged relatives.

Based on the type of genetic material exhibited by each person, a siblingship index is determined. If the siblingship index is less than 1.00, this indicates non-relatedness. If the siblingship index is greater than 1.00, this indicates that the two tested individuals are more likely to be true full sibling or half siblings. The higher the value of the siblingship index, the greater the likelihood that the two individuals are true biological relatives.

Private Home Sibling DNA Testing

Bio-Gene will only perform home Sibling tests using our 41 marker test. Our sibling DNA test examines a much higher number of markers than the industry standard, and the reason for this is that we have found lower marker tests often require additional tested parties (higher cost to you and often more difficult to get additional potential siblings/family members to cooperate) and can still come back with inconclusive results many times. Our goal is to always do what is in your best interest.


How a Home Sibling DNA Test is Performed

The most accurate method of testing is to use a buccal swab, which is similar to a “Q-tip”, which has been rubbed on the cheeks of the mouth of those being tested. We provide these with our collection kits. However, sometimes it is not possible to obtain a buccal sample. We are able to test alternative samples, normally at no extra cost. The sample should be stored in a paper envelope or breathable environment for best results. The sample should not have been stored in a plastic bag at any time. If you have questions, please call one of our Certified DNA Examiners to discuss your particular sample prior to ordering a test.

Some of the alternative samples that can usually be tested include:

Amniotic Fluid Cups / Bottles Feminine Hygiene Razors
Bandaid (Used) Dental Floss Fingernails Tissue
Chewing Gum Earwax Hair (With Root) Toothbrush
Cigarette Butt Electric Razor Hat (Well Worn) Toothpick
Condom (Used) Envelope / Stamp Pacifier Underwear


Disclaimer: Although the items listed are excellent examples, we cannot guarantee there will be a usable DNA sample on a non-standard item.


Once all DNA samples have been received by the lab, processing begins. Each person’s DNA profile is extracted and compared to the other person(s) DNA to determine the number of genetic markers that match. Using a complex algorithm the determination is made as to the probability of  biological relationships.

Sibling DNA Test Results

We write two conclusions in our reports. The first conclusion assumes that the participants have one common parent (usually a mother) in common, and gives the probability of whether they are full siblings. This testing is performed on all sibling cases, even when there is already knowledge that at least one parent is not biologically related. This portion of testing allows us to then perform testing for a half-sibling relationship.
The second conclusion assumes that the participants do not share at least one common parent and reports the probability of whether they are half siblings or unrelated. We are therefore able to get a result that will show you are not related, or you have a very high probability of being sibling (the highest possible in testing is 99.9%)

Please take a moment to review some of our case studies. The benefits of testing more markers can be found in the multiple cases in each scenario. If you have any questions, be sure to consult with a Case Manager at 1-844-246-4363.

Bio-Gene DNA’s 44 Marker Sibling DNA Test

The following information helps to understand the difference between 16 marker test (used by most testing companies) results and our 44 marker test results.

Case 1

This case illustrates why testing more markers will produce more accurate results. Samples were voluntarily collected from our lab employees and their families and then sibling comparisons were performed. One case stood out because two sisters, that were known to be FULL siblings were being reported as having a 95.39% probability they were half siblings when using the industry standard 16 marker test. Why did the 16 marker test produce a result that was false?  Sibling DNA testing is based on statistics and, with such a limited number of data points, in the case only 16 markers, the statistics were wrong. In order to lower the possibility of this happening, Bio-Gene has chosen to only perform tests with more DNA markers, or data points. When we examined these sisters using our 44 marker test, we found the probability to be 97.15% that they were full siblings, which was already known to be true.

case 1

Case 2

The two siblings in this case were adults whose parents were deceased. They had different mothers and wanted to know if they were half siblings. They had always had a suspicion that they might not share the same father and turned to DNA testing to put their minds at ease. The results of the 16 marker test found that the probability of being unrelated was only 78.83% and it seemed that their suspicion might be correct. However, the percentage was not high enough to conclusively say they were not related. When the 44 marker test was applied to their case, it was found that the probability they did not share the same father was 98.66%.

case 2

Case 3

In this sibling case, the purpose of testing was to determine if the two possible siblings were half siblings or unrelated. In this case, both mothers also contributed samples. It was reported that the probability they did not share the same father was 71.67% after testing all four people with 16 markers. A percentage this low cannot be trusted as it is not a conclusive result. After testing with the 44 marker sibling test, the results indicated that the probability of being unrelated increased to 99.96%.


Case 4

Two men had the same mother and the standard 16 marker sibling test was performed. It was found that the probability of being half siblings was only 75.23%, which is an inconclusive result. When the 44 maker sibling test was used, they were found to more likely be half siblings at 99.77%.


The conclusion that can be drawn from these cases is that a 16 marker DNA Test will not be sufficient, in most cases, if a conclusive result is desired.


How to Order a Sibling DNA Test

To order your Sibling DNA test kit, please complete the order form below and you will be taken to our secure server.  Our prices can be found by selecting the test of your choice, the number of people testing, and your payment preferences when providing the information that is relevant to your particular case.

When ordering a sibling test you may choose to use a testing kit from Bio-Gene DNA or build your own kit. This may be especially helpful is you are using alternate samples, or do not wish to the kit to arrive due to time constraints.

If you chose to use a Bio-Gene DNA Sibling Test Kit, you will choose the shipping option that is right for you. Once your kit is mailed, you will be provided a tracking number to be able to determine when it will arrive. We do not ship kits without a tracking number to protect your personal information.

If you choose to use your own kit, you will choose the “own kit” option when choosing the shipping options, and upon receipt of your order you will be e-mailed a submissionform, a unique ID number that relates to your case (we cannot process any test without this), instructions on how to collect the samples, and our lab’s address to send your completed kit with samples for immediate processing.


Make Your Own DNA Kit Instructions

Requires cotton swabs (e.g. Q-Tips) and envelopes for each participant.

submission envelope

Please follow the following steps to collect the DNA sample. When finished with one person, repeat for other participants. Collection should take 5 to 10 minutes per person:

Step 1: Swab the inner cheek

  • Swab inside the cheek with medium pressure for twenty (20) seconds.
  • Repeat using the other end of the cotton swab on the same person.
  • You are collecting skin cells, not just saliva. Use enough pressure to ensure you gain cells without harming the individual.

Step 2: Seal inside a standard sized paper envelope

  • Place the single cotton swab into a standard envelope.
  • Do NOT use plastic bags.
  • Seal the envelope with tape. Please don’t lick the envelope, as it can affect the DNA sample.

Step 3: Write the details on the  envelope detailing the sample

  • Case ID. Provided by confirmation email.
  • Collection Date. The date you collected the sample.
  • Phone. Please provide the phone number associated with your order. We will only call if there is an issue with your sample.
  • Name. First and Last. Please print clearly, this name will be shown as given on the official Bio-Gene DNA Testing report.
  • Date of Birth. The participant’s date of birth. Used in calculation.
  • Role. How this participant relates to the other samples. Choose from: Alleged Father, Child, Mother, Grandmother, Grandfather, Aunt, Uncle, Sibling, Other (Explain).
  • Race. Dominant race of participant. Choose from: Asian, African American, Caucasian, Hispanic, Native American, Other (Explain). Used in calculation.

Complete steps 1-3 for each person separately.

Step 4: Combine and send the samples

  • Place all sample envelopes into a main mailing envelope. Upon payment for your order, you will be provided with a unique Case ID to identify your case and the mailing address for submitting your DNA samples.
  • Use a reliable mail carrier to send your samples. We suggest express shipping with tracking.

If you have questions you can e-mail us at, or you may call one of our Genetic Consultants at 1-844-246-4363 to discuss your case confidentially.