. . "Vectors may be derived from bacterial plasmids, from bacteriophage, from yeast episomes, from yeast chromosomal elements, from viruses such as baculoviruses, papova viruses, such as SV40, vaccinia viruses, adenoviruses, fowl pox viruses, pseudorabies viruses and retroviruses, and from combinations thereof such as those derived from plasmid and bacteriophage genetic elements, such as cosmids and ph" . .