Mice are particularly valuable in identifying human genes, because genome organization corresponds so closely between the two species. Mammalian genomes are all derived from the same original mammalian chromosome set. Take that set, cut it into about 150 pieces, and shuffle the pieces. One way produces a human, another way, a mouse. Databases match human and mouse genes.
Many anatomical structures are similar between the species, too.
Mouse variants arise in several ways. It appeared in a stock at the Jackson Laboratory in 1990. Radiation or chemicals also are used to induce mutations. In 1993, the Jackson Laboratory started the Mouse Mutant Resource to distribute induced, transgenic, and knockout mice from research labs. We set up outside committees that meet once a month to consider new admissions.