Mutations in the pax6 gene causes developmental defects in the eyes of flies, mice, and humans. this suggests that:
a. pax6 has been evolutionarily conserved.
b. pax6 activates multiple genes.
c. pax6 may be a master regulator of eye development.
d. all of these choices are correct.

 All of these choices are correct.

Explanation:

Paired box 6 also known as Pax6 is an evolutionarily conserved transcription factor that plays a major role in the development of the vertebrate eye and the central nervous system. Mutations in mammalian Pax6 are characterized by eye defects, e.g (congenital cataracts, as well as Central Nervous System disorders like microcephaly, dysgenesis, neuron to glia transformations, etc.)  Many studies have demonstrated the importance of Pax6 to vertebrate cell differentiation, proliferation, patterning. etc

Pax6 have the tendency to  activate multiple genes. For example, if  two fly Pax6 genes, eyeless (ey) and twin of eyeless (toy), (initiate eye specification), and,  eyegone (eyg) and the Notch (N) pathway, (independently regulate cell proliferation). Pax6  have the tendency to controls eye progenitor cell survival and proliferation through the activation of eyegone (eyg) , thereby indicating that Pax6 initiates both eye specification and proliferation.

Also, Pax6 is considered to be the master control gene for eye development in all seeing animals. In vertebrates, it is required not only for lens/retina formation but also for the development of the central nervous system.