APPENDIX I 



Centrosome, the self-propagating body which, during mitosis in many 



organisms, hes at the two poles of the spindle and appears to deter- 



nine its formation. Bovcri 1885. 

 Certation, competition between pollen tubes, having different geno- 

 types, leading to their having unequal chances of accomplishing 



fertilization. Herihcrt Nilsson 1920. 

 Character, a property of an organism in regard to which (genetic) 



similarities or differences of individuals are recorded. May be either 



a Complex or Unit Character. 

 ■^"^ (chi^), the ratio of an observed sum of squares to the appropriate 



or corresponding variance as fixed by hypothesis. 

 Simple ■^^, one in which the observed sum of squares is based on a 



single comparison {i.e. one Degree of Freedom). The square of 



a Normal Deviate. 

 Compound ■)(^, one in which the observed sum of squares is 



based on several independent comparisons (several Degrees of 



Freedom), and which can therefore be resolved into two or more 



simple ;^"'s. 

 Chiasm A, an exchange of partners in a system of paired chromatids, 



observed between diplotene and the beginning of the first anaphase 



in mtiosh. Janssens 1909. 

 Classes of single chiasmata {Darlington 1929) are: — 



1. Interstitial, where there is a length of chromatid on each side of 

 the chiasma. 



2. Lateral, where the chiasma is terminal as to two chromatids and 

 interstitial as to two others. Of two kinds, symmetrical and asym- 

 metrical. 



3. Multiple, where a terminal chiasma engages three or four pairs 

 of chromatids. 



4. Terminal, where an exchange occurs amongst the end particles 

 of the chromatids, following tcrminalization. 



Classes of pairs of chiasmata [Darlington 1937) are: — 



CoMPARATE and Disparate, where pairs of successive chiasmata com- 

 pensate and do not compensate, respectively, for one another in 

 regard to the changes of partner which produce them. 



CoMPARATE chiasmata, according to the Crossing-Over wliich deter- 

 mines them, may be: — 



Reciprocal, 2-strand crossing-over, regressive. 

 Complementary, 4-strand crossing-over, digressive. 



Disparate chiasmata, 3-strand crossing-over, progressive, diagonal. 



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