Abstract

Introduction There are now a number of hints indicating that functional genes can naturally spread across species boundaries. The existence and mechanism for such transfer are well documented, especially in the prokaryotic world. In bacteria transfer of DNA is facilitated by plasmids, by phages or by direct ingestion. The genes can be established within the cell by a variety of means. If they are on a plasmid, they can be replicated autonomously, and if they are on a nonreplicating molecule, they can be incorporated into the bacterial chromosome, either by general recombination or through the action of transposable elements. Transposable elements are genes which are capable of moving from one chromosome to another (Kleckner, 1981). If we then consider the fact that the transposable elements have the ability to pick up the normally stable chromosomal genes when they move (Guarente et al., 1980) we can see how it is possible to transfer any gene among many differen

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