APPENDIX I 



Univalent, a body at the first meiotic division corresponding with a 

 single chromosome in the mitotic complement, especially when 

 unpaired. Bivalent, Trivalent, Quadrivalent, Quinquevalent, 

 Sexivalent, Septivalent, Octavalent, etc., arc associations of 

 chromosomes held together between diplotene and metaphasc of 

 the first division of meiosis usually by chiasmata. Trivalcnts and 

 higher associations are collectively termed Multivalents. 



Unstable Gene, v. Gene. 



Variability, the capacity of an individual or group of individuals to 

 produce gametes having genotypic variation. Mather 1941 ; a priori 

 the distinction can be made {Fisher 1930, Mather 1943) between: — 

 Free Variability, that which is expressed phenot)^pically, and 

 Potential Variability, that which is not expressed in the phenotypes, 



owing to dominance, etc. 

 Flow of Variability, the movement of variability in a population 

 from Free to Potential and vice versa. 



Variance, Mean Square deviation of a variate from its mean. Estimated 

 as the Mean Square. The square of the Standard Deviation. Though 

 strictly a parameter the name is commonly apphed to a statistic 

 {i.e. as synonymous with mean square). 



Analysis of Variance, a technique for the isolation of particular 

 components of variation for assessment by comparison with Error 

 Variance. Especially appHcable to the analysis of Factorial Experi- 

 ments. 



Variance Ratio (V.R.), the ratio of two estimated variances. Twice 

 the natural antilog o( z. Sometimes denoted by F. 



Variate, a variable quantity whose measurements or frequencies form 

 all or part of the data for analysis. 



Variation, i. The occurrence of differences in the permanent {i.e. self- 

 propagating) structures of cells (genotypic and heritable). Darlington 

 1929. 



2. The occurrence of differences between individuals due to differences 

 between the permanent structures of their cells (phcnotypic and 

 heritable) or to differences in external conditions (phenotypic and 

 non-heritable). 



Discontinuous Variation, where gradations of difference are per- 

 ceptible in the phcnotype. 



Continuous Variation, where gradations of difference are imper- 

 ceptible in the phcnotype. 



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