Scientists have studied patterns of development and differentiation of cells and tissues in a wide variety of species. Which statement describes the role and function of master control genes, or Hox genes, in many species?
A. They often are identical and perform identical functions in different species.
B. They are unique and perform different functions in different species.
C. They exist and function only in humans and a few other species.
D. They exist and function only in insects and a few other species.