Final answer:
In the situation where X inactivation occurs exclusively to paternally derived chromosomal zones in marsupials, only the paternally inherited genes will always be expressed.
Step-by-step explanation:
Marsupials have a unique process called X inactivation, where one of the X chromosomes in each cell is inactivated during early development. This inactivation is random, but once it occurs, all cells derived from that one will have the same inactive X chromosome. As a result, the genes on the inactivated X chromosome are not expressed.
Therefore, in the situation where X inactivation occurs exclusively to paternally derived chromosomal zones, the paternally inherited genes will always be expressed. The genes from the inactive X chromosome will not be expressed.