Solution

Double dominance is the condition that require presence of two genes to have dominant phenotype. Achondroplasia, also called as double-dominant syndrome is the example of double dominance which requires presence of two genes to produce the related phenotype. Gene responsible for organ differentiation do not show double dominance. Complementary genes are the one that produce qualitatively distinct effects when present together which is distinct from their individual effects. Plastids are the plant specific cell organelles that have different pigments; they are grouped according to the type of the pigments they have. Chloroplast is a type of a plastid. It is not found in animal; hence, $$Drosophila$$ does not have it. Homoeotic genes are the genes that regulate the development of body patterns during the organ differentiation. Hence, correct answer is B.