Grandparent, sibling and aunt/uncle DNA tests
The alleged father is deceased, unreachable, unwilling, or out of the country. His parents, siblings, or other children carry half of his DNA on average, and the laboratory can compare them with the child to assess the relationship. This guide explains who to test, what the report will and won't say, and how to avoid running the wrong combination.
Relationship test, two participants, legal or private · report typically 3 to 5 business days
Book a relationship test, $449Case design confirmed with the laboratory before your appointment · mother included free · additional participants $129
Who can be tested instead of the father
- Both paternal grandparents (grandparentage test). The strongest indirect option. Between them the alleged father's parents carry all of the DNA he could have passed on, so the laboratory can reconstruct his likely contribution with confidence.
- One paternal grandparent. Possible, and common when only one is living or willing. The result is less conclusive than with both, and including the child's mother matters much more.
- A full brother or sister of the alleged father (avuncular test). The aunt or uncle shares about half of their DNA with the father. Useful when no grandparent is available; again, the mother's participation strengthens it.
- Another child of the alleged father (siblingship test). Two children compared to see whether they share a father. The test can also distinguish full siblings from half siblings when the shared mother participates.
- Half sibling test. Two people who may share one parent. This is one of the harder questions in relationship testing; the known parent's sample is close to essential for a clear answer.
What does not work: samples from personal items (toothbrushes, hair, clothing), testing anyone without their consent, or a second-degree relative on the mother's side to answer a paternity question. If the alleged father is deceased, we are happy to talk through which living relatives could be tested; we do not arrange samples from medical examiners or exhumations.
Why these reports read differently
A direct paternity test compares a child to the alleged father and typically reports a probability above 99.9% or a 0% exclusion. A relationship test compares the child to someone who shares only part of the father's DNA, so the laboratory reports a likelihood that the tested people are related in the way claimed versus unrelated, expressed as a probability and a relationship index. Those numbers are often decisive, sometimes moderate, and occasionally inconclusive. Three things move them in your favor:
- Test the closest relatives available. Both grandparents beat one; a full sibling of the father beats a half sibling.
- Include the child's mother. Her sample lets the laboratory subtract her contribution and look only at the paternal half. She is included at no charge at the same appointment.
- Add a participant when the laboratory recommends it. Sometimes a second relative ($129) turns a moderate result into a clear one. We tell you this before you pay, not after.
We design the case with the laboratory first
Because the right combination depends on who is available, we confirm the case design with the laboratory before your appointment. Book online or send us the situation: who the alleged father is to the child, which relatives are available, and whether the result needs to be legal. We come back with the recommended combination and the exact price, then hold your time. Relationship bookings made on short notice may be moved a day so this step happens first; it prevents a wasted appointment.
Legal or private
Relationship tests can be run under full chain of custody (ID verification, neutral witnessed collection, sealed samples, notarized report) when a court, agency or attorney will rely on the result, for example in inheritance, survivor-benefit or custody matters. The price is the same either way. If there is any chance the result will be used officially, choose legal, because a private result cannot be converted later. See how legal testing works in California. We do not perform immigration DNA testing, which has its own required process.
Who attends and what to bring
- Everyone being tested at the same appointment where possible, each with government photo ID.
- For a minor, the consenting parent or guardian with ID. If the parents are not married to each other, the child's mother consents.
- Any court order or agency letter that describes what is required.
- If a participant lives elsewhere and truly cannot attend, tell us; some cases can be coordinated, and we will say plainly if yours can't.
At a glance
Relationship cases take slightly longer than paternity cases because the laboratory runs extended analysis.
Typical combinations
Child + both paternal grandparents, mother included: strongest.
Child + one paternal grandparent, mother included: good.
Child + father's full sibling, mother included: good.
Two children, shared mother included: good for full vs half sibling.
Two possible half siblings, no parent available: often inconclusive; ask us first.
Relationship testing questions
Can a grandparent DNA test prove paternity?
It can show, usually with high confidence when both paternal grandparents and the mother participate, whether the child is biologically related to the alleged father's parents, which answers the paternity question indirectly. The report states a probability of relationship rather than a probability of paternity. With one grandparent the result is weaker but often still decisive.
Do the grandparents have to be on the father's side?
Yes. Testing the mother's parents tells you nothing about the alleged father. It has to be his parents, his full siblings, or his other children.
Does a half-sibling DNA test work?
Sometimes. Half siblings share about a quarter of their DNA, and unrelated people can share a similar amount by chance, so the laboratory needs help: the shared parent's sample, or a second relative. With a parent included the result is usually clear; two possible half siblings alone is often inconclusive, and we will tell you that before you book.
The alleged father has passed away. What are my options?
Test his living relatives: his parents first, then his full siblings or his other children, with the child's mother included. We do not accept samples from personal belongings and do not arrange samples from a medical examiner. If there is an estate or benefits matter, ask the court or agency what testing it requires and choose the legal version.
Can a sibling test tell full siblings from half siblings?
Yes, when the shared mother participates. Without her the laboratory can usually still assess whether the two are related, but distinguishing full from half sibling is much harder.
How accurate is a relationship DNA test?
The laboratory reports a likelihood for each case. Well-designed cases, with close relatives and the mother included, frequently exceed 99% probability of relationship; poorly designed ones can come back inconclusive. That is why we confirm the design with the laboratory before you pay.
Can I use a relationship test for immigration?
No. Immigration DNA testing follows a separate government-directed process that we do not perform. We test for personal knowledge, court, agency and benefits matters within California.
Tell us who's available. We'll tell you what to test.
Send the situation through the contact form, or book and we'll confirm the case design with the laboratory before your visit.
Book a relationship test