  We develop a simple model to study the effects of an applied force on the
melting of a double stranded DNA (dsDNA). Using this model, we could study the
stretching, unzipping, rupture and slippage like transition in a dsDNA.
  We show that in absence of an applied force, the melting temperature and the
melting profile of dsDNA strongly depend on the constrained imposed on the ends
of dsDNA. The nature of the phase boundary which separates the zipped and the
open state for the shearing like transition is remarkably different than the
DNA unzipping
