Can you have different sets of DNA?

Most people have one unique set of DNA that’s the same in every cell of their body. However, in some rare cases, a person can have two (or more) different sets of DNA.

This can happen naturally before birth, during pregnancy, or even after a medical procedure such as a transplant.

Here we explain how and why this happens – and what it can mean for DNA testing.

What does it mean to have different sets of DNA?

Your DNA is your body’s unique genetic code. It’s found in almost every cell and determines traits such as your eye colour, blood type, and more.

Usually, all your cells carry the same DNA. Having “different sets of DNA” means that some or all of your cells have a slightly different genetic code.

This is rare, but it can happen for several reasons.

Is it possible for one person to have two sets of DNA?

Although rare, it is possible for one person to have two sets of DNA.

There are a few ways this can happen:

• Chimerism – when a person has two sets of DNA.
• Mosaicism – when changes happen in a person’s DNA after they start developing, so some cells are different.
• Transplants – such as bone marrow or stem cell transplants, which can introduce donor DNA.
• Pregnancy-related changes – where cells are shared between a mother and baby.

What is chimerism and how does it occur?

Chimerism can happen when two fertilised eggs (embryos) join very early in pregnancy and form one baby instead of twins.

The result is a person whose body contains two different sets of DNA – one from each embryo.

Other possible causes include:

• A “vanishing twin” – where one twin is absorbed by the other in early pregnancy.
• Medical transplants – if donor cells become part of the recipient’s body.

Most people with chimerism don’t know they have it, as it usually causes no health problems. It’s often discovered by chance during DNA testing.

How common is chimerism in humans?

Chimerism is extremely rare. Only a small number of confirmed cases exist, and most are only found during specialist testing.

In most cases, the differences between DNA types are small and don’t affect health or appearance.

Can a bone marrow, stem cell or organ transplant change your DNA?

Yes, but usually only in certain parts of the body.

• After a bone marrow or stem cell transplant, the donor cells produce new blood cells that carry the donor’s DNA.
• In an organ transplant, some cells from the donor may remain in the new organ and show up if the organ is tested.
• If blood is tested following a recent blood transfusion, the donor’s DNA may be detectable.

This means that a DNA test using blood after a transplant or transfusion might show the donor’s DNA instead of your own. Or a mix of both people’s DNA.

However, other cells (like those from the cheek or nails) would usually still carry your original DNA.

Can pregnancy cause different DNA in the body?

Yes. During pregnancy, a small number of cells can pass between the mother and baby.

This is called microchimerism.

• Some foetal cells can remain in the mother’s body for years.
• Some maternal cells can remain in the child’s body after birth.

This is completely normal and doesn’t cause harm.

Can identical twins have different DNA?

Although identical twins come from the same fertilised egg, they can have small genetic differences.

These changes happen naturally as the twins develop and are caused by random genetic mutations. They don’t usually affect appearance or health, but it means identical twins aren’t always 100% genetically the same.

Learn more: Can identical twins look different?

Can mutations cause different DNA within the same person?

Yes. This is called mosaicism.

It happens when a change occurs in a person’s DNA after they begin developing in the womb. That change is passed on to the new cells that grow from it, meaning some parts of the body have slightly different DNA.

For example:

• One patch of skin might have a small genetic difference from another.
• A person might carry both normal and altered cells in their blood.

This usually has no noticeable effect on a person’s health or appearance.

How can having two sets of DNA affect DNA testing?

Having more than one set of DNA can sometimes make DNA test results confusing.

For example:

• A cheek swab might show one DNA type, while a blood test shows another
• In very rare cases, it could make a paternity or relationship test appear to show no match when one exists

This is why AlphaBiolabs’ scientists review every result extremely carefully and may recommend additional testing if needed – though this is extremely rare.

Can your DNA change over time?

No, your DNA doesn’t usually change but some cells can develop minor differences as you age.

Would having two sets of DNA affect a paternity test?

Having two sets of DNA could affect a paternity test, but only in rare situations. If a person has chimerism or has had a bone marrow transplant, certain samples might show a different DNA type.

Our sample registration forms ask whether the donor has had a bone marrow or stem cell transplant or whether they have any other genetic conditions that may affect the test so this can be taken into consideration by our expert analysts.