Source(s): immigration nationality directorate border immigration uk border agency reference no: https://tinyurl.im/UEZro.
About 99% of mouse genes have a homolog in the human genome, and for 80% of these genes, the best match in the human genome has, in turn, its best match against the orthologous mouse gene in the conserved syntenic interval.
Mice are more brown to begin with, and have darker bellies. Next is the tail. It's black with scaley rings on a rat, and tan and more smooth on a mouse. The feet of a rat are also longer in proportion to the body, and a rat's ears are also larger. But these variations are subtle. The primary thing, of course, is the size difference.