describe the three stages in sexual reproduction and mention the major events in each of them
Answers
These events of sexual reproduction are prior to the fusion (fertilization) of male and female gametes.
These events are gametogenesis and gamete transfer.
The process of formation of two types of gametes—male and female is called gametogenesis. Gametes are haploid cells. In some algae, the two gametes are so similar in appearance that they are called homogametes (isogametes; Fig. 1.29), e.g., Cladophora, Ulothrix. Therefore, it is not possible to differentiate them into male and female gametes.
However, in most of sexually reproducing organisms the gametes are of two morphologically dissimilar types hence they are known as heterogametes (anisogametes), e.g., Fucus (a brown alga), humans. In these organisms the male gamete is called the antherozoid or sperm and the female gamete is known as the egg or ovum (Fig 1.29 B.C).
Cell Division during Gamete Formation:
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Gametes are haploid whether the structures or cells producing them are haploid or diploid. The structure formed by the fusion of gametes is always diploid. It is due to meiosis which occurs in the life of all sexually reproducing organisms. Gamete producing cells which undergo meiosis are called meiocytes (gamete mother cells). The latter are diploid. .