The abdominal segments of Drosophila have no appendages. Loss of function of bithorax genes results in appendages forming in these abdominal segments. Therefore, __________
A) bithorax mutations are necessarily recessive
B) bithorax genes normally activate appendage-forming genes
C) ultrabithorax usually acts to oppose bithorax genes
D) bithorax normally activates a gene that negatively regulates appendages in the abdomen
E) expression of bithorax wild-type genes suppresses all appendage formation
D
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