sex, or reproductive, cell containing only one set of dissimilar chromosomes, or half of the genetic material necessary to form a complete organism (i.e., haploid). During fertilization, male and female gametes fuse, producing a diploid (i.e., containing paired chromosomes) zygote. Gametes may be identical in form (isogamy), as in the black mold (Rhizopus), or there may be more than one morphological type (heterogamy), as with many green algae of the genus Chlamydomonas. Gametes of animals, some algae and fungi, and all higher plants exhibit an advanced form of heterogamy called oogamy. In oogamy, one of the gametes is small and motile (the sperm), and the other is large and nonmotile (the egg). See also egg; sperm.