Progressive Retinal Atrophy (PRA) in dogs is an autosomal recessive genetic disorder that causes progressive blindness.
A breeder crosses two healthy Labrador retrievers. Each of these parent dogs had one parent that suffered from PRA (and was therefore homozygous recessive for the condition).
What is the probability that a litter of 3 puppies from this cross will contain exactly 1 healthy puppy and 2 puppies affected by PRA?
364\frac{3}{64}643
38\frac{3}{8}83
2764\frac{27}{64}6427
964\frac{9}{64}649
