In this scenario, what color mice is more “Fit”?
Fit/Fitness- Organisms which are better
suited to their environment

It's cell theory. easy name i would think.

When a virus infects a host cell, it uses the cell's machinery to make copies of its own genetic material in a process called replication. finally, during the process of self-assembly, that protein shell and the copies of the virus's genetic material are assembled into new viruses.