Simultaneous assessment of average fragment size and amount in minute samples of degraded DNA

There is currently no method allowing routine characterization of minute amounts of degraded DNA samples such as those encountered in forensic science, archived tissues, ancient DNA, extracellular or stool DNA, and processed food. Here we describe and directly validate such a method based, on the one hand, on a generalized DNA random fragmentation model and, on the other, on two quantitative polymerase chain reaction (PCR) experiments using two different target sizes. The model also makes it possible to determine the minimum sample amount, the minimum mass average fragment size, and the maximum degradation time necessary to obtain a positive PCR.