Answer:
The correct answer would be -
Punnett square is given below and on the base of the result of Punnett square, Millie should mate with Denver to get three different colors of puppies.
Step-by-step explanation:
The question says that Millie has a genotype BB*, which is a combination or heterozygous condition of dark brown allele B and white allele B*, now cross with Denver (light brown color):
Cross 1:
B B*
B BB BB*
B* BB* B*B*
the results is : 25% dark brown, 50% light brown and 25% white.
cross 2: with Charley (white color)
B B*
B* BB* B*B*
B* BB* B*B*
there is only white and light brown puppies produced
Thus, the correct answer is - Denver.