The ability to extract and PCR amplify DNA from biological stains
is a key element in Forensic Genetics. Fortunately DNA often
survives for months or years at ambient conditions in untreated dry
stains.1e6 The effects of various parameters on the survival of DNA,
such as UV-light, stain substrates, admixture of soil, age, humidity,
and temperature have been previously assessed.2,6e9 However, to
the knowledge of the authors there is little information about the
stability of DNA in stains when controlled conditions of humidity
and temperature approach the extreme. Microbial enzymatic attack
is of fundamental importance in the degradation of organic
matter10 but depends, among else, on the availability of water. Also
many of the non-enzymatic processes that degrade DNA depend on
the presence of water.11,12 A priori one would therefore expect an
accelerated rate of degradation of DNA in biological stains as the
relative humidity approaches 100%. To determine the range of
natural conditions that allow an adequate stability of DNA in stain
material, blood stains without any stabilizing additives were
incubated at various conditions of relative humidity (RH) and
temperature. The quality and quantity of the remaining DNA was
estimated by the ability to PCR amplify long and short fragments
and by quantitative assessment using real time PCR.