It has been reported that some people have two different sets of DNA, and if they do, they are known as human chimeras. 

Insider writes, in Greek mythology, a chimera was a fire-breathing creature with physical traits of a lion, goat, and dragon. However, human chimeras develop naturally, and some people aren’t even aware that they have doubles up on DNA.

You can end up as a human chimera in the following ways: 

After a bone marrow transplant

During bone marrow transplants, doctors use chemotherapy or radiation to destroy all of the recipient’s diseased bone marrow, then a donor’s healthy marrow is put in its place. 

The donor’s bone marrow will keep on producing blood cells that have the donor’s DNA, according to a Scientific American report. Therefore, the recipient becomes a chimera. 

A paper in the journal Nature went on to explain that in “complete chimera,” 100% of the recipient’s blood cells have the donor’s DNA. But, the blood can also contain a mix of DNA from the donor, as well as the recipient. This is otherwise known as “mixed chimerism.”

When fraternal twins are in utero

Scientific American explains, when a mother is carrying fraternal twins, one of the embryos might die very early in the pregnancy. As a result, the other embryo can absorb some cells from the deceased one, causing it to end up with two sets of DNA.

During a normal pregnancy

Back in the 90’s, scientists discovered that a pregnant woman may retain some DNA from her baby, that’s if some fetal cells migrate outside the uterus. Scientifically this is known as “microchimerism.”

A simple way to prove this is to test the mothers of boys and see if they have any cells with Y chromosomes, which are only present in males. In one particular study, researchers sampled tissue from 26 women who had died during pregnancy or just after giving birth to a boy. In every sample, they found low concentrations of cells with Y chromosomes. 

Similarly, a different study looked at the brains of mothers who had boys. They discovered traces of male DNA in 63% of the women, even in a woman who was 94 years old, Scientific American reported. This extended finding, suggests that microchimerism might continue to exist after pregnancy.