  We consider birth-and-death stochastic evolution of genotypes with different
lengths. The genotypes might mutate that provides a stochastic changing of
lengthes by a free diffusion law. The birth and death rates are length
dependent which corresponds to a selection effect. We study an asymptotic
behavior of a density for an infinite collection of genotypes. The cases of
space homogeneous and space heterogeneous densities are considered.
