Et eksempel på horisontal genoverførsel er at fremmed [[DNA]] kan komme fra [[parasit]]ter, f.eks. at 70% af [[hvirvelløse dyr]] har indlejret store dele eller næsten hele parasitten ''Wolbachia''s [[genom]] i deres genom.
<ref>[http://www.sciencedaily.com/releases/2007/08/070830150118.htm University of Rochester (2007, August 31). One Species' Entire Genome Discovered Inside Another's. ScienceDaily. Retrieved November 10, 2007] Citat: "..."This study establishes the widespread occurrence and high frequency of a process that we would have dismissed as science fiction until just a few years ago," says W. Ford Doolittle, Canada Research Chair in Comparative Microbial Genomics at Dalhousie University, who is not connected to the study. "This is stunning evidence for increased frequency of gene transfer."..."This parasite has implanted itself inside the cells of 70 percent of the world's invertebrates, coevolving with them. And now, we've found at least one species where the parasite's entire or nearly entire genome has been absorbed and integrated into the host's. The host's genes actually hold the coding information for a completely separate species."..."</ref>
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