An animal exhibits a normal appearance if it possesses either two normal genes or one normal gene and one mutated gene. However, if both genes are mutated, the animal will appear mutated. Each parent has a 50% likelihood of passing on either of its genes to its offspring.
Consider animals A and B as the parents of C and D. Subsequently, C and D are the parents of E. Both A and B carry one normal gene and one mutated gene. It is observed that both C and D appear normal. What is the probability that D carries one normal gene and one mutated gene, given that E appears normal?