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Understanding your DNA test results

Understanding Your DNA Results

Your DNA test report shows the results of our AABB laboratory partner’s DNA findings that provide genetic evidence regarding the alleged family relationship you requested testing for. This guide is a brief explanation of the meaning of the numbers (that is to say, the statistical certainty of the result) and other items that appear in your DNA test report:

The laboratory analysis uses the DNA isolated from cheek swabs, or other samples if you chose to test a non-standard DNA sample. A non-standard sample is anything other than a mouth swab, or a FTA (blood) card which is usually obtained from a medical examiner.

The DNA was extracted and examined to locate certain regions of chromosomes that are known to vary in length between individuals. Each region (site) is called a “locus”, (“loci” – plural). 24 of these sites are tested; Analysis of these 24 sites in a large population has revealed many different sized versions associated with each site. Versions of a DNA sequence or a gene are called “alleles.” These are the genetic markers used in parentage analysis.

In some cases, the lab may have chosen to do extended testing, up to 35 loci. This usually occurs when a conclusive result is not able to be reached. Extended testing may be done more with sibling, grandparent, and avuncular tests.

Because each individual has two of each type of chromosomes, one inherited from each parent, everyone has two alleles at each locus. These two alleles are sometimes identical (homozygous), but usually they are not the same size (heterozygous). During paternity and relationship DNA testing, the laboratory identifies the length of the two alleles found at each locus.

Each locus used in DNA testing is composed of a variable number of repeating short sequences of the DNA building blocks or “bases”. These are referred to in “DNA shorthand” as “A”, “C”, “T” and “G”.

An example of a natural DNA sequence having such simple short repeats would be ACGACGACGACG, i.e. (ACG)4. However, each allele can have a different number of total repeats, for example (ACG)3 or (ACG)5 instead of (ACG)4, giving rise to a different fragment length when the DNA is purified and amplified in the test tube. In this example, (ACG)3, (ACG)4 and (ACG)5 would encode variant alleles with building block lengths of 3 x 3, 4 x 3, and 5 x 3, that is 9, 12, and 15 building block lengths. Since DNA analysis machines detect changes in length of just one unit, these differences in length are easily distinguished.

The columns on the DNA test report contain numbers indicating the two alleles found at each locus (or one number if they are the same size). If, for example, in a paternity test, a child has two alleles that are designated 12.1 and 18, and if the mother has alleles 12.1 and 16, then the child inherited the 12.1 allele from the mother. The child has to have inherited the 18 allele from the father. The 18 allele is the “obligate paternal allele.” Generally, the alleged father must have this allele if he is the biological father of the child.

In the example below, 23 different loci are used as genetic markers in the DNA tests, as well as one (Amelogenin) to confirm the sex of the person providing the DNA sample. This makes a total of 24 markers tested.

Journey Genetic Testing DNA Report

If the DNA of the alleged father is consistent (to a degree of mathematical certainty) with that of the child, then the report will conclude that the alleged father cannot be excluded as the biological father of the child. If the DNA is not consistent however, it will conclude that the alleged father is excluded as the biological father of the child.

Combined Paternity Index

A combined relationship index for the tested alleles is then calculated and appears on the report. This number is used to calculate the “probability of paternity/relationship,” which is likelihood that a man with the alleles of the alleged father is the biological parent of the child, as compared to an untested, unrelated man of the same race, shown as a probability percentage.

Paternity test result showing the man in not the father

Paternity/Maternity Testing Results

In a paternity or a maternity test, whether for personal knowledge or court admissibility, there are three possible outcomes.

 o Excluded. The probability of paternity will be 0.0%. This means that the alleged parent is NOT the biological parent of the child. This occurs when an alleged parent’s DNA does not match on at least 22 of the 24 tested genetic markers.

 o Cannot be excluded. The probability of paternity/maternity will be at 99% or greater. This means that the alleged parent is, in all reasonable probability, the biological parent of the tested child. 99.99+% and higher is the greatest probability that science can provide for proof of relationship. In legal cases, most courts accept a probability of at least 97% as proof that the tested male/female is the biological parent.

o Inconclusive. This is extremely rare and occurs in cases where insufficient DNA has been provided for one or more of those being tested. This result would require a re- submission of DNA samples.

Kinship Testing: Sibling/Grandparent/Avuncular (Aunt/Uncle) Results

The results will be stated as a probability of either being biologically related or unrelated for the specific relationship tested for. This type of relationship testing does not determine if there may be a biological relationship other than the specific test ordered. Testing companies that issue results showing a variety of possible relationships cannot state with any degree of certainty that any of the possibilities listed are actually accurate. That is why the type of testing you had done can be trusted in the findings as we compare person to person for a specific relationship.

Each test begins with a 50/50 chance of either verifying or excluding the relationship. This is indicated with as a .5 prior probability. Each marker tested has a specific probability assigned to it, which may be show as a CRI (combined relationship Index), or sometimes a SI (sibling index), GI (grandparent index) or AI/KI (avuncular/kinship index). These numbers determine the statistical probability of the relationship being tested for. The higher the probability, the more likely the relationship. The lower the probability, the less likely that a relationship exists. AABB standards state that a 91%% probability of relationship is the minimum probability percentage needed for a confirmed relationship, and a 9% or less probability shows the likelihood of an exclusion of the relationship.

91% – 99.9+% – The genetic evidence indicates the tested relationship is confirmed.

9%-90.9% – Findings in this probability range are uncommon, but can occur in genetic testing. The genetic evidence cannot support or deny the relationship tested for. It is suggested that additional family members have their DNA submitted for a more conclusive result. A mother’s DNA does help to minimize the possibility of this type of finding in sibling, grandparent, and aunt-uncle testing.

9%-0% – The genetic evidence does not support the existence the biological relationship tested for.

The reports that Journey Genetic Testing’s partner laboratory delivers are the most accurate results available, using the highest number of markers approved by the AABB for relationship testing. The percentages reported are the same for both personal knowledge and legally admissible results, with the exception being that the legally admissible testing has followed proper collection guidelines, and completed the needed documentation required for court ready DNA testing reports.

Sibling DNA Test Results

A full sibling test report will show the results as a probability of the two siblings being full siblings. If the probability range is 91% or greater, then the genetic evidence from the DNA samples tested support both siblings having the same biological mother and father. If the findings are in the 9% or lower range, then the genetic evidence does not support full siblingship, but would indicate the likelihood that the siblings only share one biological parent and are half siblings.

A half sibling test will show the results of two or more people testing who know they do not share both biological parents and are wanting to determine if they share one parent. This is usually the father, but may also be the mother in cases of adoption or other uncertainty surrounding the relationship. A half sibling relationship can be said to be supported by the DNA evidence if the relationship probability is 91% or greater. A 9% or lower probability does not support a half sibling relationship.

Grandparent and Avuncular DNA Test Results

A Grandparent DNA test, or an aunt/uncle aka Avuncular DNA test, will show that the genetic evidence supports the relationship tested for if the findings show a probability of 91% or greater. If the report shows a relationship probability of 9% or less, the relationship is not supported by the DNA submitted. If the test result shows inconclusive, even after testing additional markers, please consider adding an additional person to the test for a stronger result. If the mother of the child did not test, her DNA should be considered to be added. If she is not available, please contact us for other recommendations, by completing a support ticket with your case number.

Y-STR Male Lineage Results

If the testing results find they cannot be of the same male linage then there is no paternity of the alleged father if performing this test for paternity purposes.

If the testing indicates that they cannot be excluded from being of the same male line, and if being done to establish paternity, they the probability indicated is the likelihood that the alleged father is the biological father.

Twin Zygosity Test Results

A twin zygosity test shows with complete accuracy whether the two or more siblings tested are either identical (monozygostic) or fraternal (dizygostic) twins. If all of the generic markers tested match at every location, the report will show a 99.9+% or greater probability of being mono-zygostic. If there is not a match at even one location they siblings are not identical twins.

Why can’t the test results show 100% probability of being identical twins? The analysis required for zygosity testing is all about statistics and the only way the twins could be statistically listed as 100% probability is if every person in the world with the same ethnic background were also tested. Of course, this is impossible, so the results have to reflect the mathematical findings.

What If My Results Are Inconclusive?

While an inconclusive result is not common in Kinship Testing, it can occur depending on the genetic profiles obtained at the time of processing the samples. This is also explained in the Terms of Service agreed to at the time of your order.

The possibility of an inconclusive result is greatly decreased when a mother’s DNA sample is submitted as her DNA is then “subtacted out” of the genetic profiles of the child being tested, to only focus on the non-parent’s contribution.

In those uncommon cases where the results do not fall into a conclusive percentage, and a mother’s DNA was not included with the original samples for testing, is suggested that the person who ordered the test consider adding a mother’s DNA to help bring about a stronger result. If the mother is not available, or additional parties need to be added, please contact us for other suggestions. There will be a lab processing fee for additional samples submitted, as testing will need to be run again, however we will work with you to find the most suitable person to submit for additional testing.

If a mother’s DNA is added at the time of the original order, there is no additional charge to include her DNA in the testing. If the mother’s DNA is to be added after the testing has been completed, there is a charge of $125 to include her DNA and run additional testing. This includes a prepaid UPS overnight mailer for samples to be returned.

If this is something you choose to have done, you may do so by CLICKING HERE. We will the name and shipping address of the mother whose DNA will be submitted. Once payment confirmation is received. we will authorize the processing of the new order.

How Long Do I Have To Add Another Person To My Test For New Results?

You have 30 days from the date the results are delivered to add a person to the testing. The cost to add a person after the testing has been completed, and new testing run, is $125.00. If this is what you wish to do, we will need the name and address, as well as the suspected relationship, of the person to be added to the testing, You may order an additional person be added to your test by CLICKING HERE. Once payment confirmation is received, your request will be processed.

Journey Genetic Testing reserves the right to not accept any additional individuals to a completed or in process test. The decision of Journey Genetic Testing will be final in these cases.

What Are The Different Symbols On My Test?

(x) Identifies exclusion(s) at the system(s) indicated. When a parentage test shows that the alleged parent is eligible to be the biological parents at all but one or two loci, we consider the possibility that they may be the biological parent but a mutation has occurred. MORE INFO:

(n)  Identifies null (silent) allele at the system(s) indicated.  Alleles that do not amplify during the   PCR process. When this occurs, a weighted average of all alleles in the locus indicated is used to complete the calculation.


(mb) Identifies multi-band (tri-allele) allele at the system(s) indicated. Triallelic patterns can be due to length mutations that occur and segregate during an individual’s development, or to localized duplication of a locus, or to chromosomal trisomy.


(Xm) In a paternity test trio, indicates a mutation between the mother and child. This system is calculated as a duo (between alleged father and child).


(Xp)    In a maternity test trio, indicates a mutation between the father and child. This system is calculated as a duo (between alleged mother and child).


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