5. You cross one black (Bb) mouse with one brown (bb) mouse. Complete the Punnett square to find the expected ratio of black to brown mice pups. All six mice pups in the litter have brown fur. Explain this result.

I think all the mice had brown fur due to epistasis

Explanation:

The expected results would be 50% black and 50% brown and the ratio could be 2:2.  But, if epistasis occurred and the brown fur gene overshadowed the black fur gene, then all the offspring could have brown fur.  

ability to bond woth oxygen