Como podrías justificar que el ser humano y el ratón tienen aproximadamente 80% de similitud en la información genética

Both species are mammals and therefore they share genome regions and gene families that are conserved in the course of evolution.

Explanation:

Synteny enables to identify conserved genome regions between species by aligning their DNA sequences. For example, the human and chimpanzee genomes share about 95-98% of synteny (sequence similarity) in their DNA sequences. In this case, a whole-genome sequence similarity of 80 % is evidence that both species are relatively closely related and share a near common ancestor. Indeed, it is expected that the most part of the remaining 20% represents mutations associated with the fixation of neutral alleles (i.e., neutral mutations) and therefore have no evolutionary meaning.

multiple allele inheritance is traits controlled by more than 2 alleles (ex: pigeons having 3 alleles of one gene govern their feather color).   so the answer is a.