Gametes (3)
I believe the answer is:
ova
'gametes' is the definition.
(ovum is a kind of gamete)
This is all the clue.
(Other definitions for ova that I've seen before include "Latin egg-cells" , "Female reproductive cells" , "Prerequisite for procreation" , "Potential life sources" , "Likely end for Russian Fed cup players" .)