Knight — 60 — Dictionary 



Gene Starvation, Theory of. — A theory put forward by 

 Thompson (1938) suggesting that to reproduce itself nor- 

 mally a gene must have available in its vicinity all the neces- 

 sary 'parts'. Lack of any 'part' during the stage between suc- 

 cessive nuclear divisions is suggested as the cause of muta- 

 tion, or alternatively of gene deficiency, at the 'starved' locus. 

 On this theory, differential nutrition in the early stages of 

 segmentation of the fertilized ovum gives rise to mass muta- 

 tion in certain groups of cells from which are produced the 

 primordia of the differentiated adult tissues. 



Gene String. — The central chromosome thread on which the 

 genes are, assumedly, arranged in sequence. 



Gene Substitution. — The replacement of one gene by its 

 allele, all the other genes (or all other relevant genes) remain- 

 ing" unchanged. 



Genecology. — (i) A combination of genetics and ecology; 

 the study of the interactions of environment and genetic con- 

 stitution, (ii) Ecology which is mainly concerned with species. 



Genepistasis. — The concept that evolution may often long 

 remain at a standstill at a definite stage. 



Generational Sterility. — Basic, inherent sterility due to 

 such causes as an unbalanced chromosome number, or lack 

 of homology as between the two chromosome sets in an in- 

 terspecific hybrid, as opposed to sterility due to malformed 

 anthers or pollen incompatibility. 



Generative Apogamy, — Reduced apogamy ; haploid parthe- 

 nogenesis. See under Parthenogenesis. 



Generative Apospory. — The formation of gametophytes 

 from archesporial cells or their derivatives which lack the 

 character of spores (Fagerlind). 



Generative Nucleus. — The gametic nucleus of a pollen grain 

 as distinct from the vegetative or tube-nucleus. 



Generitype. — The type species of a genus. 



Genetic Complex. — A collective term for all the hereditary 

 factors borne in an organism. 



Genetic Factor. — Gene, q.v. 



Genetic Isolation. — Separation of groups by the formation 

 of inter-group sterility barriers. 



Genetic Polymorphism. The co-existence of two or more 



genetically-determined and well defined forms ("phases") of 

 a species in the same area (Huxley). 



Genetic Variation. — A heritable variation produced by a 

 change in the genes, e.g. a mutation, deletion, recombination, 

 etc. 



