Yes, possible DNA sequences do not occur with equal frequencies. The whole point of selection pressure is that it selects for specific sequences. The same seque

Yes, possible DNA sequences do not occur with equal frequencies. The whole point of selection pressure is that it selects for specific sequences. The same sequence occurring in a host species and a parasite is also not surprising. Rare events could result in horizontal transfer of genetics between host and parasite. Such things have been documented before.