Half Sibling DNA Test – All You Need To Know

There could be many reasons why you may want to look into a DNA siblings test.

It could be for the peace of your own mind, or to determine if you and your sibling are full or half-siblings!

You may need to submit a siblingship test for legal purposes or for an immigration application.

So, if you have planned on taking the sibling DNA test, you must be anxious and definitely have many questions running in your mind.

You are in luck! I did my research and I have gathered up some information about the DNA test and what you should be expecting.

So, read through the article and your anxiety will be at ease.

You will surely feel a lot more confident.

Half Sibling DNA Testing In General

Half Sibling DNA Testing In General

When two people are suspected to have the same father and they know they have different mothers, they will not necessarily have the exact paternal DNA as one another.

This is because each of the child (or your sibling) receive a random 50% of your biological father’s DNA.

Only identical twin shares the exact same genetic DNA profiles.

Hence, this is why more extensive analysis is often recommended in half sibling cases.

Sibling DNA testing is pretty much a very simple test nowadays and is carried out to determine the relationship between two people to assess if they are siblings.

Now let us have a closer at the half sibling DNA test.

For a half sibling DNA test it is assumed that the mother is not shared, but the question is do you share the father in common or not.

So, if you do share the father in common, then the test results will indicate it.

The test also determines the following:

  1. whether two people are full siblings; two or more individuals share a parent or two.
  2. Or whether two people are half sibling; two or more individuals share one biological parent.
  3. Or not siblings at all!

So, after being tested, your results will give you your required answers.

Half Sibling vs Full Sibling Analysis

In a half sibling DNA test it is assumed that one parent is different while one parent is the same (do not share the same mother but want to verify that they do share the same father)

On the other hand, in a full sibling DNA test it is assumed that both the parents are shared (do share the same mother but need to confirm that they also share the same father)

When the status of the known parent is unknown such in the case of an adoption, we can perform both a full sibling and a half sibling DNA test.

Types of (Half) Sibling DNA Testing

The test is divided in two types:


Let us start with the At Clinic Sibling DNA Testing

Sibling DNA Test at the Clinic

The sibling DNA test at the clinic is the legal test, which is done when you schedule an appointment and pay for it at any authorized lab for the people.

What type of sample is collected in a legal test and who needs to be tested?

The most common sample type is a buccal swab.  This sample is collected using a cotton swab that is gently rubbed on the inside of your cheek.  Blood samples are also acceptable.

To perform the test, you need to make sure the right people are present with you before the test.

The following people need to be present:

  • The potential siblings
  • Any available parents – for example a shared mother, or if testing if two individuals are half siblings, both mothers.

The mothers just add to the tests reliability and results come out more conclusive.

How reliable are the results?

The likelihood of obtaining a conclusive result when undertaking a sibling test varies depending on which individuals are participating in the case.

When testing if two individuals are Full or Half Siblings:

  • Two Siblings and one shared parent – 96%
  • Two Siblings – 78%

When testing if two individuals are Half Siblings or are Unrelated:

  • Two Siblings and both mothers – 94%
  • Two Siblings one of their mothers – 86%
  • Two Siblings – 73%

Reasons you might need a Sibling DNA Test:

There could be many reasons why you would want to or need to get a Sibling DNA Test done.

It could be:

  • For personal family matters
  • For confirmation if two or more siblings share one or two parents
  • For legal purposes like presenting an evidence to court for parentage established or other legal matters.
  • For an immigration application or appeal
  • For CRBA or passport
  • For the embassy USCIS/ICE or Dept. Of Homeland Security
  • For child support or visitation rights
  • For name change on birth certificate
  • For social security benefits
  • For estate planning or probate
  • Or for any case where proving the relationship through an accredited DNA test is required

All these official reasons require the legal sibling DNA test results only.

The witness

For a legal sibling DNA test, you will be required to show proof of witness.

Only a medical professional from a doctor office or clinic may be the witness for your legal DNA test.

Now we move to our second type of Sibling DNA Testing which is the At Home Sibling DNA Test.

Sibling DNA Test at home?

At-home DNA tests are commonly called non-legal tests because their results cannot be submitted for any legal documentation or legal reasons.

DNA samples for at-home tests are collected by individuals in the privacy of their own home.

The most common question that most people ask is that “If we share on parent, shouldn’t half of our DNA match?

Well, I am here to tell you that this is not how since works.

However, this is only true for identical twins. Only they inherit the same DNA from heir mother and father.

Full siblings and half siblings share the DNA to some extend only, like for half siblings about 25% of DNA is expected to match.

However, this also varies.

It is true that we inherit half (50%) of our DNA is from our mother and other half (50%) is from father. This is why paternity and maternity testing is always most conclusive and recommended type of DNA testing.

But for other DNA testing like half sibling DNA testing or full sibling DNA testing, complex scientific algorithms are used to produce the percentage of probability based upon how many markers of the participants match or do not match.

In short:

  • Identical Twins share 100% of the genes.
  • Full Siblings share 50% of the genes.
  • Half Siblings share 25% of the genes.
  • 1st Cousins share 12.5 % of the genes.

Acceptable samples for a home-based DNA Test

If you are unable to provide with the usual cheek swab, or buccal swab, for the DNA test.  a cheek swab.

Then in such cases, forensic processing services for other types of DNA samples is offered.

Other DNA samples may include the following:

  • Ear wax
  • Hair (must be plucked and have the root ball attached)
  • Mucous on a tissue
  • Finger or toenail clippings
  • Toothbrushes

These are often the common forensic samples.

Although, in certain cases where the relative is deceased, tissue or blood samples may be available from a medical examiner or coroner’s office.

Non-legal tests vs legal ones

At home Sibling DNA test provide the same information as a legal DNA test, but they are not intended for use in a court of law.

They are only for personal knowledge.

Legal sibling DNA tests provide you with a fully accredited, notarized result that is admissible court approved evidence.

If there is a possibility that the results might be needed for legal purposes, a legal test should be performed.

So, if you need to get a legal test done you should visit your local laboratory where they perform legal sibling DNA test.

Other Analysis Tests

If tested individuals have related mothers and they want to see if they have the same father, or believe their fathers could be related, half sibling DNA testing may not produce the most accurate result.

A sibling DNA test is also not a reliable option if there is a cousin relationship in the case.

So, what is the solution here?

Well then in this case, a paternity or maternity test with the parent in question would be the best solution.

A male lineage Y-STR test for males, or an mtDNA female lineage test to look for a common female line may be a better testing option


This option is if the half siblings are both male and would like to see if they have a common father, a Y-STR test is a very accurate and conclusive test to consider.

It is recommended over the half sibling test when the mothers are not included.

The Y-STR test compares the Y-Chromosome every father passes to his male child.

When Y-STRs for two males are compared, the result will be basically a “Yes” or “No” answer to the question of whether or not the two tested males related through the paternal line.


The gender of the siblings does not matter for this maternal mtDNA testing.

If the half siblings would like to see if they share a relationship on the maternal side, an mtDNA test is recommended.

MtDNA test provides a conclusive answer regarding a common female lineage similar to the Y-STR testing for males.

In addition, there are other tests that may be more conclusive based on who is available to test.

For example:

  • the grandparent DNA testing for an alleged grandparent and grandchild
  • the avuncular aunt/uncle DNA test with a full sibling of the alleged parent

It is also okay to consider a family reconstruction test if more than one paternal relative is available to participate in a DNA test.

Why is it best to include the mother(s) in the half sibling test?

It is always recommended to include both or at least one of the mothers if it is possible.

Because including the mother makes it easier to compare mother and child as it eliminates all the DNA the child has inherited from the mother.

Which leaves the rest of it in the profile of that half sibling test participant is from their father.

So then, the remaining paternal DNA from one half sibling to the paternal DNA of the other possible half sibling are compared together.

This highly increases the conclusive and accuracy of the test.

In general, if the mother(s) are available for testing they should be included if possible.

Although the test can still be performed without the inclusion of the mother(s) if one or both are not available but if this is the case, then you should consider running the extended analysis which will test up to 35 markers for more conclusive results.

However, for conclusive and more accurate results for half siblings DNA test, both at clinic and at home tests, it is best to include mother(s) in the testing.

Summing Up

Both the half siblings DNA tests; at home and at clinic give accurate results. Their procedures are also similar.

But the main difference is that at home half siblings tests can not be used for legal reason.

If you are required to do a legal half sibling DNA test, then you must visit a laboratory.