It's the scientific name of the Black rat. It belongs to under the kingdom of Animalia. It is also known as roof rat, ship rat, or house rat. It is a long-tailed rodent. They are black to light brown with a lighter color underside. There is another type of black rat called Tamed black rats. They are sometimes kept as pets.
Black rats are generally omnivorous. They are harmful to farmers because they eat various types of crops. So, for removing Black rat from the crop fields, farmers follow different types of protective ways.
It can't really be codominant since lowercase letters are recessive, and condomance needs 2 dominant alleles of a different types. So really it should be BB for blue, RR for red and BR for patchwork...