facio-orbital bristles (ARTHRO: Insecta) In Diptera, bristles on each side near the orbit, may extend to the gena or cheek; orbital bristles. see genal bristles.
factor n. [L. facere, to do, to make] 1. An agent or causative agent in genetics determining development of a hereditary character in offspring. 2. (PORIF) A cell surface-active proteoglycan affecting the stability of cell-to-cell adhesion.
facultative n. [L. facultas, capability] The ability to live under different conditions. see obligate.
facultative meiotic parthenogenesis The diploid chromosomal complement in the reduced oocytes is restored by fusion of the second polar nucleus with the egg pronucleus. see automictic meiotic parthenogenesis.
facultative parasite 1. A parasitic organism that can develop inside a host, but still retains the ability to complete a free-living life cycle in the outside environment. 2. Organisms normally free-living that may become parasitic under special environmental conditions. see obligate parasite.
facultative symbiont A symbiont that establishes a relationship with a host only if the opportunity presents itself. see obligate symbiont.
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