Black-Cheeked BC Zebra Finches Are Extremely Desirable, but Relatively Rare

Black-cheeked BC zebra finches are extremely desirable, but relatively rare. This phenotype is caused by a recessive mutation, but the mating of two BC birds is considered unethical because it results in very small birds. Therefore, BC birds are created by crossing carriers of the BC gene. Despite problems with the homozygous recessive, some unscrupulous breeders continue to breed them together because of the high prices they fetch. Which of the following statements could explain why BC homozygous birds are unusually small?

A) The BC gene causes a mutation in a growth gene.
B) The BC gene and a gene for growth are very close to one another on the same chromosome.
C) The BC gene and a gene for growth are both mutated.
D) The dominant version of the cheek color gene (GC) encodes a gene for normal size.
E) The BC gene and growth gene are close together on the same chromosome and/or both of these genes are mutated.