In Chlorophyceae, sexual reproduction occurs by isogamy, anisogamy or oogamy.
Isogamy: The gametes are similar in size and shape. These gametes are not classified as male or female.
Anisogamy: It is the fusion between two gametes which are either dissimilar in size or in both size and morphology. It is observed in Chlamydomonas.
Oogamy: Oogamy is a type of anisogamy. The male gamete is smaller in size than the female gamete.