Question

Write a note on sexual reproduction in protists.

Answer 1

In protists, sexual reproduction involves two fundamental processes; meiosis, that reduces the number of chromosomes from 2n to 1n and fertilization or fusion of two 1n gametes to form a 2n zygote (fertilized egg). Meiosis is essential in sexual reproduction since it reduces the chromosome number to half in gametes so that after fertilization the number of chromosomes is kept constant in a species. There are two methods of sexual reproduction:

1. Syngamy: It is complete fusion of two gametes to produce a diploid zygotes. Syngamy is of three types: (i) Isogamy (two fusing gametes are similar e.g., Monocystis); (ii) Anisogamy (two fusing gametes are dissimilar, e.g., Ceratium) and (iii) Oogamy (large non-motile gametes are fertilized by smaller motile gametes, e.g., Plasmodium).
2. Conjugation: It is temporary union of two individuals to exchange their haploid pronuclei to form a zygote nucleus. Each individual with zygote nucleus produces produces daughter individuals by binary fission. It occurs in Paramecium.