Birthplace of Columbus (5)
I believe the answer is:
'birthplace of columbus' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for genoa that I've seen before include "North Italian port" , "Cake type; foresail" , "City of Italy" , "Italian city has no age, oddly" , "Seaport in northwestern Italy" .)