Correct Option: A

Isogamy refers to a form of sexual reproduction involving gametes of the same size. Since both gametes look alike, they cannot be classified as “male” or “female.” Instead, organisms undergoing isogamy are said to have different mating types, most commonly noted as “+” and “–” strains. Fertilization occurs when “+” and “–” strain gametes fuse to form a zygote. There are several types of isogamy. Both gametes may be flagellated and thus motile. This type mating occurs in algae such as Chlamydomonas.

A. Isogamy of motile cells
B. Isogamy of non-motile cells