![](http://www.ncbi.nlm.nih.gov/books/NBK26860/bin/ch24f36.jpg)
Drawing of an experiment that directly demonstrates that DNA is rearranged during B cell development
The B cell tumor arose from a single B cell and therefore makes a single species of antibody molecule. The two radioactive DNA probes used are specific for the DNA sequences encoding the C region and the V region of the light chain that the tumor cells make.