Deletions in mice in the Hoxa3 gene, on the A cluster, result in abnormal formation of glands in the ...

Deletions in mice in the Hoxa3 gene, on the A cluster, result in abnormal formation of glands in the neck. Deletions in the homologous Hoxd3 gene, on the D cluster, result in abnormal formation of the neck skeleton. The protein-coding sequences of Hoxa3 and Hoxd3 are about 50% the same. Researchers inserted a functional copy of the coding sequence of Hoxd3 in place of the coding sequence of a nonfunctional Hoxa3. They left all promoters, enhancers, splicing signals, and processing signals of Hoxa3 in place. Normal neck gland development was restored. What can you conclude? (J. M. Greer, J. Puetz, K. R. Thomas, and M. R. Capecchi. 2000. Maintenance of functional equivalence during paralogous Hox gene evolution. Nature 403:661-65.)
A) The protein-coding sequence is most important in producing different functions.
B) Regulation of the genes is most important in producing different functions.
C) Either A or B could be true.