Chlamydomonas isogametes
   are  haploid  and consist of opposite mating types: plus (+) and minus
   (-).

<bR>The  isogametes are morphologically and genetically indistinguishable,
   differing only in surface chemical makeup.

   Mating  (fertilization)  only  occurs between + and - cells, which can
   fuse to form a diploid zygote.