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Events of Sexual Reproduction

This includes formation of gametes (gametogenesis) and their transfer (gamete transfer)...

Events in Sexual Reproduction

Events in sexual reproduction may be grouped into three distinct stages as follows:

  1. Pre-fertilization

  2. Fertilization (also known as syngamy)

  3. Pre-fertilization


This includes formation of gametes (gametogenesis) and their transfer (gamete transfer).

Gametogenesis: It involves formation of two haploid reproductive units called gametes. The formation of haploid male gamete (sperm) from the diploid spermatogonia is called spermatogenesis.

Gamete transfer: After gamete formation, male and female gametes must be physically brought together to facilitate fusion (fertilization).

Fertilization or syngamy:
  • It is the fusion of male and female gametes to form a diploid cell called zygote.

  • The phenomenon in which the female gamete undergoes development to form new organisms without fertilization is called parthenogenesis, e.g., rotifers, honeybees, lizards and birds.

  • Fertilization is of two types, i.e., external fertilization and internal fertilization.


Events in sexual reproduction after the formation of zygote are called post-fertilization events.

These include development of zygote and embryo after fertilization.

Development of zygote: In external fertilization, zygote is formed in the external medium, whereas in internal fertilization, zygote is formed inside the body of the organism.

Embryogenesis: The processes of development of embryo from the zygote is called embryogenesis.

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