All the offspring of a white hen and a black rooster are gray. The simplest explanation for this pattern of inheritance isa. pleiotropy.b. sex linkage.c. codominance.d. incomplete dominance.

Step by Step Solution: Step 1. Identify the pattern of inheritance. In this case, the white hen and the black rooster produce gray offspring, which suggests that there is a blending of traits. Step 2. Eliminate answer choices through process of elimination. Answer choice B and E are not applicable in this case, as there is no special association with either sex chromosome or multiple genes. Answer choice A suggests that a single gene is responsible for more than one trait, which is not applicable here. Codominance and incomplete dominance both show a blending of traits, but the most appropriate answer choice is incomplete dominance because the blending is not complete, and the intermediate phenotype is observed. Step 3. Therefore, the correct answer is option D, incomplete dominance. Final Answer: The simplest explanation for the pattern of inheritance is incomplete dominance.