Knight — 62 — Dictionary 



individual gene; a mutation proper, transgenation or point 

 mutation. 



Genuine Pleiotropism. — The controlling, by a single gene, 

 of "two (or more) different effects which it produces directly 

 and by the use of different mechanisms. Spurious pleiotropism 

 may be brought about in two ways. Either the gene does two 

 (or more) things directly, but by means of the same mechan- 

 ism, or else it has one effect which in turn causes other things 

 to happen" (Gruneberg). 



Geoclines. — The graduations of variation produced within a 

 species by adaptation within an area showing geographical 

 variation extending over considerable distances. 



Geographical Divergence. — The evolution from a single 

 ancestral form of two or more different forms, subspecies, or 

 species, each in a different geographical area. 



Geographical Race. — "A complex of interbreeding and com- 

 pletely fertile individuals which are morphologically identical 

 or vary only within the limits of individual ecological and sea- 

 sonal variability. The typical characters of this group of in- 

 dividuals are genetically fixed and no other geographical race 

 of the same species occurs within the same range" (Rensch, 

 quoted by Mayr, 1942). 



Geographic Speciation. — The gradual formation of new 

 species by reason of the spatial isolation of different stocks 

 of the original species. 



Geratology. — The study or science dealing with senescence 

 and decadence. 



Germ Cells. — Gametes, or cells which give rise to gametes. 



Germen. — The reproductive glands. 



Germinal Selection. — Selective competition as between 

 gametes. 



Germinal Spot. — The nucleolus of an unfertilized tg^. 



Germinal Vesicle. — The nucleus of a primary oocyte. 



Germplasm, — The material basis of heredity. Weismann's 

 term for the hereditary substance in the germ-cells; idioplasm. 



Gerontic. — Appertaining to senescence or decadence. 



Gerontomorphosis. — Evolution which is brought about by 

 variations affecting adult organisms and which is characterized 

 by increasing specialization and a decreasing capacity for 

 further evolution. The production of phylogenetic effects by 

 the modification of characters which were already present in 

 the ancestral line of adults. 



