When both alleged grandparents participate in testing, their DNA can be examined together to identify the alleles that their biological child, the untested alleged parent, could have inherited. This is called a genetic pool analysis.
This section explains whether the grandchild’s DNA is compatible with that combined genetic pool. It is separate from the individual statistical analyses for each grandparent, which appear elsewhere in your report.
What is a genetic pool?
At each DNA marker, also called a locus, a person normally has two alleles: one inherited from their biological mother and one from their biological father. An allele is a version of a DNA marker and is represented by a number in the report.
The untested alleged parent would have inherited one allele from each of their biological parents. By testing both alleged grandparents, the laboratory can identify the possible alleles that this untested parent could have inherited.
For example:
| Person | Alleles at one DNA marker |
|---|---|
| Alleged grandfather | 12, 15 |
| Alleged grandmother | 13, 19 |
| Combined genetic pool | 12, 13, 15, 19 |
The untested parent would have inherited one of the grandfather’s alleles and one of the grandmother’s alleles. Their possible allele combinations would therefore be 12/13, 12/16, 15/13 or 15/16.
The combined pool lists possible alleles. It does not mean the untested parent has all four alleles, and it does not establish their exact DNA profile.
How is the grandchild compared with this pool?
The grandchild inherits one allele at each marker from each biological parent.
If the tested grandparents are the biological parents of the grandchild’s biological parent, at least one of the grandchild’s alleles at each marker is expected to appear in their combined pool, apart from possible mutations.
The grandchild’s other allele comes from their other biological parent and does not need to match the pool.
Using the example above:
| Grandchild’s alleles | Comparison with the pool of 12, 13, 15, 16 |
|---|---|
| 12, 18 | Compatible: allele 12 is in the pool. |
| 13, 15 | Compatible: both alleles are in the pool, although only one needs to match. |
| 14, 17 | Incompatible: neither allele is in the pool. |
What does “Not Excluded” mean at a marker?
“Not Excluded” means that the grandchild’s DNA is compatible with the grandparents’ combined pool at that particular marker.
It does not mean that the relationship has been confirmed. Alleles are shared throughout the population, so people who do not have the proposed biological relationship can still match at individual markers.
A “Not Excluded” entry therefore means that the marker does not rule against the proposed relationship on the basis of this pool comparison.
What does “Excluded” mean at a marker?
An “Excluded” entry means that neither of the grandchild’s alleles at that marker appears in the grandparents’ combined pool. This is a mismatch, or genetic incompatibility, at that particular marker.
For example, if the grandparents’ pool contains 12, 13 and 15, but the grandchild has 14 and 17, neither of the grandchild’s alleles could be passed down from that pool through ordinary inheritance.
“Excluded” in an individual row describes the finding at that marker. It is not, by itself, the overall conclusion of the grandparentage test. The laboratory considers the findings together, including possible mutations and the limitations of the analysis.
Why can the overall result be unfavourable when most markers say “Not Excluded”?
The result is not determined by counting whether there are more matching markers than mismatching markers.
Matches are possible between people who do not have the proposed relationship. In contrast, a marker where neither of the grandchild’s alleles appears in the pool presents an incompatibility with the expected inheritance pattern.
For this reason, many “Not Excluded” entries do not cancel out the significance of multiple mismatches. A report can contain mostly compatible markers while the combined findings weigh against the proposed grandparent relationship.
Could a mismatch be caused by a mutation?
Yes. A mutation is a change in DNA that can occur when genetic material is passed from a parent to a child. It can occasionally produce a mismatch even when a biological relationship exists.
This is why a single mismatch should not be interpreted on its own. The laboratory evaluates the pattern across the tested markers rather than assuming that every mismatch proves the absence of a relationship.
Multiple mismatches can provide evidence against the proposed relationship. Their interpretation depends on the findings as a whole.
What does “more unlikely than likely” mean?
When the report states that the tested pair are more unlikely than likely to be the biological grandparents, it means that the laboratory’s overall interpretation weighs against the proposed grandparent-pair relationship.
It does not mean that every marker failed to match, and it should not be interpreted as the same definitive exclusion that may be obtained through direct DNA paternity testing.
The genetic pool table also does not, by itself, provide a percentage probability. Refer to the report’s stated conclusion and statistical sections rather than trying to calculate a probability from the number of matching rows.
Why is this analysis less powerful than a direct paternity test?
A direct paternity test examines the alleged father’s actual DNA profile and compares it with the child’s DNA.
Genetic pool analysis examines the DNA of the alleged grandparents instead. Their combined pool includes several alleles that the untested parent might have inherited, but it does not show which alleles that parent actually inherited or passed to the child.
This additional uncertainty makes the pool comparison less discriminating than testing the alleged parent directly. Grandparentage testing is therefore generally used when the alleged parent is unavailable for testing.
How does this differ from the individual grandparent results?
The sections examine different aspects of the proposed relationship:
| Report section | What it evaluates |
|---|---|
| Combined genetic pool analysis | Whether the grandchild’s alleles are compatible with those that could have passed through a biological child of the two tested grandparents. |
| Individual grandparent statistical analyses | The statistical evidence for a grandparent–grandchild relationship between each tested grandparent and the grandchild, considered separately. |
The combined pool analysis evaluates the proposed grandparent pair together. An unfavourable pool result does not, by itself, establish which individual grandparent is unrelated or whether both are unrelated.
For that reason, the combined pool section and the individual statistical sections should each be read according to their own explanations and conclusions.
How should I read this portion of my report?
Start with the written conclusion, then use the marker table to understand the findings that contributed to it.
Remember:
- “Not Excluded” at a marker means compatible at that marker, not a confirmed relationship.
- “Excluded” at a marker means a mismatch at that marker, not automatically a definitive overall exclusion.
- The number of matching rows is not a percentage probability of the relationship.
- The combined genetic pool result concerns the tested pair together; individual grandparent statistics are reported separately.
If you need help understanding a particular entry, contact our Client Support Team with your case number and the name of the DNA marker or report section you would like explained.