In mice, the gene C causes pigment to be produced, while the recessive gene c makes it impossible to produce pigment (albino). Another gene, B, on a different chromosome, causes a chemical reaction with the pigment and produces a black coat colour. The recessive gene, b, causes an incomplete breakdown of the pigment, and a tan colour results. The genes that produce black or tan coat colour rely on the gene C, which produces pigment, but are independent of it. The mating of a tan mouse and a black mouse produces many different offspring. One of the offspring is albino. The tan mouse is Ccbb How do you know the genotype of the black mouse? I know it's CcB? but I don't know how the ? allele is found. CcBB will produce CB, CB, cB, CB gametes and and can cross to give albino offspring that are ccBc and albino. CcBb can give offspring that are albino as ccbb. My textbook says the black mouse is CcBb since an allele must be taken from both parents. That isn't any justification for why that's the answer is it?