Write a note on pre-fertilisation.
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Answer:
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Explanation:
PRE- FERTILIZATION
The events of sexual reproduction which occurs before fertilization are called pre-fertilization events.
Pre- fertilization events are a) gametogenesis and b) gamete transfer.
Gametogenesis-
The process of formation of gametes is called gametogenesis.
Gametes are the specialized haploid cells and are of two types- male and female gametes.
Fig.male gametes, sperms are surrounding the female gametes, egg.
When both the gametes are similar in appearance that these can be distinguished, these gametes are called homogametes or isogametes. Example- algae.
fig. homogametes of algae
When both the gametes are dissimilar in appearance, the gametes are called heterogametes or anisogametes and the male gamete is called antherozoid or sperm and the female gamete is called egg or ovum. Example- human, higher plants.
Fig. heterogametes
Gametes are haploid even though the parent body is diploid.
If the parent is haploid, the parents produce gamete by mitosis. Example- monera, algae.
In diploid parents, the parents produce gametes by meiosis, the reduction division to produce haploid gametes. Example- human beings, higher plants.
In diploid organisms, the gamete mother cells which undergo meiosis to produce gametes are called meiocytes, as a result at the end of meiosis only one set of chromosome gets incorporated into each gamete hence, the gamete becomes haploid.
Human beings are diploid organisms and have 46 chromosomes and so the gametes contain 23, half of the number of chromosome by reduction division.
Gamete transfer-
The process of bringing together of male and female gamete for fertilization is called gamete transfer.