Difference between technical and biological replicates

The basic definitions of technical and biological replicates are as follows:

• Technical replicates: a test performed on the same sample multiple times; i.e., if there are triplicate non-treated samples, a technical replicate would be testing sample #1 of the non-treated multiple times
• Biological replicates: a test performed on biologically distinct samples representing an identical time point or treatment dose; i.e., if there are triplicate non-treated samples, a biological replicate would be testing sample #1, 2 and 3 of the non-treated group

Both types of replicates are necessary and add to experimental design and statistical power.  However, the simplistic definition of replicates can get complicated quickly in regards to your specific experiment.

A common problem is what defines a biological replicate in regards to in vitro cancer cells.  Is a biological replicate considered as the results from using two separate freezer stocks created in the lab or from two separate freezer stocks from the cell repository (i.e. ATCC)?  Purchasing separate stocks from the repository can get expensive.  The common solution for biological replicates in in vitro experiments is to maintain separate flasks of the same cells.  Although the cells are derived from the same source, it is accepted that the separate handling of each flask classifies it as a biologically different organism.