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Spit Our Way

February 21, 2012

Preston Estep, PhD is the Director of Gerontology and leads the saliva collection effort at the Personal Genome Project at Harvard Medical School.

We’re getting to love spit. Here are a couple of fun facts about saliva that most people (including most scientists) don’t know: most saliva is loaded with DNA, and the primary source of that DNA is blood cells. This has been shown by genotyping people with bone marrow transplants (1). The genotype of blood and saliva from transplant recipients is typically more similar to the genotype of the marrow donor than the pre-transplant genotype of the recipient (the genotype of the non-hematopoietic cells of the recipient is retained). This amazing discovery also demonstrates interesting and practical things about saliva biology, including that most DNA in it does not come from cheek or other epithelial cells. So, when we send you a collection kit there is no need to swab or abrade cheeks (or to make awful choking sounds). Just salivate and spit.

The blood origin of saliva DNA is just one reason we love spit. And we need spit. Your spit! We know most of you have sent us saliva but we need those who haven’t to spit our way. Not in our general direction, but according to our directions, which can be found on a double-sided sheet of paper included in every kit we send out. For those who have provided saliva in the recent past, fear not, you’ll get yet another chance to spit again very soon. Plus, you’ll get to use our new and improved collection kits. We understand if you can barely contain your excitement.

If you are wondering about the status of saliva samples you already submitted, you can check your sample log.  To do this, follow these steps:

  1. Log-in at
  2. Click on “Edit” Your profile at top left
  3. Scroll down to Samples and click on the “Show log” link on the right
If you’d like a more tangible link to your sample, here is a peek inside of our first dedicated saliva sample freezer:

Saliva samples donated by PGP participants in the freezer. By Preston Estep, licensed under CC-BY-SA.

If we have received your samples then they are in there somewhere. This one freezer is pretty empty and we have more to fill. We’re looking forward to you spitting our way.


1) Thiede C, Prange-Krex G, Freiberg-Richter J, Bornhäuser M, Ehninger G. Buccal swabs but not mouthwash samples can be used to obtain pretransplant DNA fingerprints from recipients of allogeneic bone marrow transplants. Bone Marrow Transplant. 2000 Mar;25(5):575-7. PMID: 10713640

One Comment
  1. March 10, 2012 5:02 pm

    I just collected my samples today! Who knew it was that difficult to conjure up a vial of saliva? Eventually I figured out that waving a tub of salsa in front of my nose expedited the process and I had no problem finishing of the samples.

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