Google Answers DNA: Mixed-Up Blood

Google Answers DNA: Mixed-Up Blood

by Dr. Hsien-Hsien Lei
Posted September 20, 2007 in DNA @ Google Answers, DNA and the Law

Google Questioner:

If someone donates blood, and that blood is transfused into someone who later commits a crime that leaves blood evidence at the scene, will the DNA of the donor be at the crime scene or only the DNA of the
person who committed the crime?

My answer:

In 2005, something very similar happened. A man who donated bone marrow to his brother several years earlier was accused of committing a sex attack in Alaska when blood tests matched his DNA profile to the crime. But, it really wasn’t him! It was his brother who committed the crime.

The mix-up resulted because his brother’s blood had some cells that contained the brother’s DNA and other cells that contained his own. Investigators were quick to catch the mistake, however, when they found that the accused was in jail at the time of the attack. Experts emphasized that the chances of this happening to other bone marrow donors were slim to none.

Google Answers found this excellent answer at the Canadian National DNA Databank:

It is possible, but unlikely. It will partly depend on the type of transfusion received. If a person has received only red blood cells (which do not contain DNA), there will be no confusion. If the person has received white blood cells or platelets (both of which contain DNA), there could be a mixture of recipient DNA and donor DNA in the sample. Upon analysis, both DNA profiles would be identified. They will not “mix” to create one, new profile.

Keep in mind that the human body will replace all transfused blood cells within three or four weeks. If the transfusion was minor, the recipient’s original DNA profile would be clearly prominent. If the transfusion was major, the recipient will probably be too ill to commit a serious crime before their body has replaced most of the donor cells.

In those rare cases where two DNA profiles are discovered in a sample, it is always noted and the analysis double checked. Investigators are also notified for further follow up as required.

So if you’re thinking of committing a crime and are prepping by doing the vampire thing beforehand, it won’t work.

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Comment by Corrine Subscribed to comments via email

Especially now that other cell types, such as buccal swabs, can be used as sample…this avoids the blood transfusion issue altogether.

Hi Corrine, Thanks for the comment! Buccal swabs are great but still doesn’t address the issue of blood left at the crime scene. Hypothetically, if there was a mixture of DNA in a patient who’d recently received a transfusion and this patient left blood at a crime scene, it could still complicate the investigation no matter how the DNA is collected from suspects.


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