Final answer:
Animals with genotype 'bb' have white fur.
Step-by-step explanation:
The fur color of animals with genotype bb is white.
In this species of mouse, the gene responsible for fur color is controlled by a single gene pair. The dominant allele B produces black fur, while the recessive allele b produces white fur. Since animals with the genotype bb have two copies of the recessive allele, their fur color will be white.