Horizontal gene transfer (HGT) from host to virus allows for AMGs to be acquired. Gene transfer from host eukaryotes to viruses occur about twice as frequently as virus to host gene transfers due to a higher number viral recipients than donors. The vast majority of gene transfer occurs in double-stranded DNA viruses since they have large and flexible genomes, co-evolution with eukaryotes, and wide host breadth. Additionally, unicellular hosts more commonly transfer genes.