That homologous recombination occurs between the targeted DNA and an introduced plasmid that is homologous to a chromosome does not require that the targeted DNA actually be chromosomal DNA. It requires only that the targeted DNA be homologous to chromosomal DNA. Non-chromosomal DNA, such as mitochondrial DNA or DNA in an additional plasmid, can be holmogous to chromosomal DNA.

Institut Pasteur & Universite Pierre et Marie Curie v. Focarino, No. 12-1485 (Fed. Cir. Dec. 30, 2013) (holding that Patent and Trademark Review Board erred in its "obviousness" analysis of patents that relate to putting genes into "eukaryotic chromosomes").