A gamete (reproductive cell) that differs in size, shape, or structure from another gamete it will fuse with during sexual reproduction.
From Greek 'anisos' (unequal) + 'gamete' (from 'gamos,' marriage/union). The term emerged in late 19th-century biology to describe the unequal sex cells observed in many organisms.
Most animals and plants have unequal gametes—the egg is huge while the sperm is tiny and speedy—but many single-celled organisms have gametes so similar you'd think they were identical twins until genetics proved otherwise!
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