DNA denaturation as a new kind of phase transition
  Unbinding of a double-stranded DNA reduces to an unscreened long range interaction and maps on various problems. Heterogeneity renormalizes interaction. Renormalization is temperature dependent. At an unbinding transition it approaches critical dimensionality. This implies giant non-universal critical indexes and invalidity of the Gibbs distribution sufficiently close to the critical temperature Tc. Fluctuations are macroscopically large below Tc. There are no fluctuations above it. 
Mark Ya. Azbel'