It certainly is possible that the North American population has to carry different mutations than a population of Norway rats in Africa. Genetic mutation is a random event, and the alleles resulting from mutation may rise in frequency and be fixed within the population if they provide a benefit to the fitness of the individuals with that allele. One random mutation could occur in the North American population and not be found in the African population because the occurrence of this mutation is random. It is also possible that the two populations carry the same mutations. This would be the case if the mutation occurred either if the mutation occurred in a common ancestor, or if the mutation occurred prior to the 2 populations becoming allopatric. By studying the genomes of each population scientists will be able to determine when certain mutations occurred. Mutations found in one population and not the other occurred more recently, while mutations found in both populations occurred further back in evolutionary time, and may have originated in a common ancestor.