The two main pre-fertilisation events are: Gametogenesis and gamete transfer.
a. Gametogenesis
Gametogenesis is the process of formation of the two types of gametes – male and female.
Gametes are haploid cells.
In some algae the two gametes are so similar in appearance that it is not possible to categorise them into male and female gametes.
They are called homogametes (isogametes).
In a majority of sexually reproducing organisms the gametes produced are of two distinct types (heterogametes).
In such organisms the male gamete is called the antherozoid or sperm
and the female gamete is called the egg or ovum .
Sexuality in organisms:
Generally, sexual reproduction in organisms involves the fusion of gametes from two different individuals
but may not be always true.
Plants have both male and female reproductive structures in the same plant (bisexual) ( or on different plants (unisexual).
In several fungi and plants, terms such as homothallic and monoecious are used to denote the bisexual condition and
heterothallic and dioecious are used to describe unisexual condition.
In flowering plants, the unisexual male flower is staminate,
i.e., bearing stamens, while the female is pistillate or bearing pistils.
In some flowering plants, both male and female flowers may be present on the same individual (monoecious) or on separate individuals (dioecious).
Some monoecious plants are cucurbits and coconuts and of dioecious plants are papaya and date palm.
Cell division during gamete formation:
Gametes in all heterogametic species are of two types namely, male and female.
Gametes are haploid though the parent plant body from which they arise may be either haploid or diploid.
A haploid parent produces gametes by mitotic division.
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