All teleost fish species have two copies of the sodium channel gene SCN4A: scn4aa and scn4ab.
a. From the evidence in Figure 15.33a, did the duplication of SCN4A happen just once in teleosts, or multiple times independently? Explain your reasoning.
b. In two lineages of electric fish, the expression of scn4aa is restricted to the myogenic electric organ. From the evidence in Figure 15.33b, did this change in expression happen just once, or multiple times independently? Explain.
c. From the evidence in Figure 15.33b, has scn4aa undergone adaptive evolution following the change in