Isogamy, anisogamy and oogamy are different forms of sexual reproduction. Syngamy or the fusion of gamete is varied according to the nature of gametes and mode of their fusion. These are the three types of syngamy.
In the isogamy the gametes are isogametes fusion occurs between the isogametes. In anisogamy the fusing gametes are dissimilar and motile i.e. is anisogamous. One of the gametes is larger than the other. In oogamy fusion occurs between the non-motile female gamete and the motile gametes.