Much later , he worked on the technique of homologous recombination of transgenic DNA with genomic DNA . This is the most reliable method of altering animal genomes at present , and the technique behind gene targeting and knockout mice . Oliver Smithies ( born June 23 , 1925 ) is a British-born American geneticist and Nobel laureate , credited with the invention of gel electrophoresis in 1955 , and the simultaneous discovery , with Mario Capecchi and Martin Evans , of the technique of homologous recombination of transgenic DNA with genomic DNA , a much more reliable method of altering animal genomes than previously used , and the technique behind gene targeting and knockout mice .