My Genome is in a Tube of Spit?

Spit has DNA? Well, not exactly. Spit has cells in it, and the cells have DNA.

For everything except bacteria (and some other types of single-celled organisms), DNA is wound up tightly inside a cellular structure called the “nucleus”. It’s actually pretty amazing how well it’s packed – the DNA of a single human cell is almost 6 feet long, but cells are able to stuff it inside a structure that is generally about 1/200 the size of the period at the end of this sentence.

When you send your spit to the 23andMe lab they get your DNA from the nuclei of cheek cells floating around in your saliva. How, you might ask, do they do that?

It’s a two-step process. First, they break up the cells and the nuclei that are inside of them in order to release your DNA, not to mention a lot of other cellular gunk. Then they isolate your DNA from all that gunk so they can use it for genotyping.

After the jump, find out how the process works, and how you can try it yourself in your very own kitchen.

You can try your hand at isolating DNA using fruit instead of human cells. The Tech Museum has detailed recipes and instructions for this at-home science activity called “DNA Spooling.”

Essentially, what you will do is smash up the fruit in a solution of salt and soap, filter out the big chunks and then add a bit of cold rubbing alcohol. If you’re careful, what you’ll end up with is a nice big gob of DNA floating at the interface between the alcohol and the soap solution. You can even stick in a toothpick and play with the DNA (I think it looks and acts a lot like snot.)

The soap/salt solution you mash up your sample acts as an “extraction buffer” that breaks up cells and nuclei, allowing access to the DNA. The rubbing alcohol “precipitates” the DNA, which just means that it makes it clump up.

The process used in 23andMe’s lab to extract your DNA for genotyping is a lot more precise (and a lot less messy) than DNA spooling, but the principles are the same.


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