  In this short note we study a dynamical system generated by a two-parametric
quadratic operator mapping 3-dimensional simplex to itself. This is an
evolution operator of the frequencies of gametes in a two-locus system. We find
the set of all (a continuum set) fixed points and show that each fixed point is
non-hyperbolic. We completely describe the set of all limit points of the
dynamical system. Namely, for any initial point (taken from the 3-dimensional
simplex) we find an invariant set containing the initial point and a unique
fixed point of the operator, such that the trajectory of the initial point
converges to this fixed point.
