<P> In plants, oogenesis occurs inside the female gametophyte via mitosis . In many plants such as bryophytes, ferns, and gymnosperms, egg cells are formed in archegonia . In flowering plants, the female gametophyte has been reduced to an eight - celled embryo sac within the ovule inside the ovary of the flower . Oogenesis occurs within the embryo sac and leads to the formation of a single egg cell per ovule . </P> <P> In ascaris, the oocyte does not even begin meiosis until the sperm touches it, in contrast to mammals, where meiosis is completed in the estrus cycle . </P>

Sperm and ova are produced through a process of reduction division called