APPENDIX I 



Post-Reduction [continued) 



2. The segregation of differences between partners at the second, as 

 opposed to the first, meiotic division. 



PoTENCE, the property of a group of Polygenes corresponding to the 

 degree of Dominance of a Major Gene. Wigan 1944. 



Precocity, the property in the nucleus at meiosis of beginning prophase 

 before the chromosomes have divided. Darlington 193 1. 

 Precocity Theory, that meiosis is primarily distinguished from mitosis 

 by showing a precocity of the prophase, which successively deter- 

 mines pairing, crossing-over, chiasma formation, non-division of the 

 centromeres and insertion of a second division, together with the 

 reduction of chromosome number and the segregation of differences. 

 Darlington 1930 . 

 Differential Precocity, the property of some chromosomes, or of 

 their parts, condensing, dividing or pairing in advance of the rest 

 of the complement during prophase. Shown by some hetero- 

 chromatic chromosomes, v. Heteropycnosis. Darlington 1937. 



Preformation, v. Epigenesis. 



Prepotency, the capacity of an individual to produce offspring more 

 like itself and less like the other parent. Practical breeder's term for 

 a property depending (where genuine) on superior homozygosity, 

 dominance and potence. 



Pre-Reduction, v. Post-reduction. 



Presence and Absence Theory, that the dominance of one allelomorph 

 is due to the presence of sometliing in it which is absent from its 

 alternative. Bateson 1909. 



Prime Type (m Datura), one of the homozygous t)^pes of chromosome 

 structure distinguished from other such types by interchange and 

 used as a basis of reference, u. Basic Type. Blakeslee 1928. 



Probability, the proportion of an infinite (and hypothetical) series of 

 cases in which an event, possible in any one of them, actually occurs. 



Probability Function, the function relating observations to the para- 

 meter from whose value their frequencies may be predicted. Cf. 

 Likelihood Function. 

 Simple Probability Function, that relating to the occurrence of a 



single event. 

 Compound Probability Function, that relating to more than one 

 event. 



Proband, Propositus. 



Prochromosome, body of Hcterochromatin seen in the resting stage. 

 Overton 1909. 



412 



