APPENDIX I 



Mutable Gene, v. Gene. 



MuTAFACiENT, of oiic geiic or genetic element which determines, or 



increases, the chance of mutation of another. Darlington 1944. 

 Mutant, aberrant individual, cell or gene produced by Mutation. 

 Mutation, a change of heredity not ascribable to segregation or recom- 

 bination. De Vries 1890. Classifiable as follows: — 



Gene Mutation, intragenic change, i.e. from one gene to an alle- 

 lomorph. A residual category after the exclusion of identifiable 

 structural changes. 



Structural Mutation, intergenic change in the hnear arrangement 

 of genes, sometimes producing a Position Effect, v. Structural Change. 



Numerical Mutation, a change in the number of chromosomes, 

 either balanced to give Polyploidy or unbalanced to give Aneuploidy. 



Plastid Mutation, a change in a chloroplast affecting its capacity to 

 produce chlorophyll, v. Plastogene. 



Cytoplasmic Mutation, a change in cytoplasmic heredity, v. 

 Plasmagene. 



Induced Mutation, determined by externally controlled conditions. 



Mutation Rate, the proportion of individuals or cells in a given group 

 wliich show mutation for a given gene under given conditions in 

 one generation, or other stated unit of time. 



Somatic Mutation, a change observed or inferred in somatic tissue. 

 Its nature is assumed from analogy with mutation in the germ track. 



Mutation Pressure, the measure of the action of mutation in tending 

 to alter the frequency of a gene in a given population. Cf. Selection 

 Pressure. Wright 1921. 



Mutation Theory, that new species arise by single mutation. De Vries 

 1890. 



Certain consequences of crossing-over and aberrant segregation 

 in hybrids have been attributed to mutation, e.g. Half-Mutation 

 {De Vries 1918) and Mass-Mutation {Bartlett 1915) in Oenothera 

 and Pseudo-Mutation in apomictics with sub-sexual Reproduction. 

 Guslafsson 1934. Attenuation and Fortification are the conse- 

 quences of mutation in viruses. 



n, gametic as opposed to 2n, the zygotic, number of chromosomes. 

 Nature and Nurture, the antithesis between Genotype and Environ- 

 ment. 

 Neomorph, v. Amorph. 

 Non-Disjunction, Bridges 1914. 

 Cytological (Numerical) Non-Disjunction, the failure of separation 

 of paired chromosomes at meiosis and their passage to the same pole. 



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