Abstract: The invention related to a method of gene targeting in a transformable host organism, and compositions useful for carrying out the method. The method of gene targeting provides improvement over previous gene targeting methods since it is generally applicable over a wide variety of transformable organisms. It provides time savings in producing organisms with specific gene modifications, and it does not require a pluripotential cell line. The targeting method of the invention exploits the endogenous cellular process of homologous recombination to implement gene targeting at essentially any known gene.