EXCLUSIVE

A piece of Farrah Abraham can be yours … and we’re not talking about her ass -- the backdoor teen mom has put her DNA on the market.

Abraham's partnered with Celebrity Gene, a company that liquefies the DNA of celebrities -- usually extracted from hair -- and puts it in a vial you can wear around your neck. Very Angelina Jolie circa 2001.

The jewelry vials go for $99, and it’s mostly for a good cause because 50% goes to the charity of the celeb's choice – in Farrah’s case, it's Operation Underground Railroad, which helps rescue kidnapped children from slavery.

We're told Abraham's also banking a 10% cut from sales ... in addition to the roughly $30,000 she got upfront for the DNA sample.

Abraham has a history with the double helix … she tells TMZ a positive paternity test changed her life and "created a better future" (aka Social Security benefits) for her daughter.