Answer:
Brown is the dominant gene and white is the recessive gene.
Step-by-step explanation:
If brown were to be dominant then the mice would most likely all be brown unless the got both a white from mom and dad which is most likely due to brown being recessive the dad could be part white you just wouldn't see it. And since the mother is white all of the mice get a white gene from the mom and since the dad most likely has a white gene hidden inside of him only tow mice became fully white while the siblings were brown.
Hope this helps.