Mustapha Mond
World Controller, Western Europe
I don't think gene-seed implants are meant to change the DNA of their subject, but they do alter the cells of the host on every level, and a certain amount of genetic affinity to the DNA of the primarch is required to make it work. Basically, the gene-seed DNA sort of "supercedes" the human DNA to turn the subject into a kind of mini-clone of the primarch.