582 APPENDIX III 



Molecular , the coiling within the chromosome thread which 



conditions internal and relational spirals. D., i935- 



(Primary and secondary coils of Kuwada and Nakamura are minor 

 and major spirals). 



Spiralisation, the assumption of an internal (but not a relational) spiral by the 

 chromatids in mitosis and meiosis. D., 1932. 



[Spireme], the chromosomes during the prophase in mitosis or meiosis, and 

 hence the prophase itself. Particularly used in the expression " con- 

 tinuous spireme." Flemming, 1882. 



Spore, a cell specialised for reproduction but not for fertilisation. In the 

 higher plants it is always the product of meiosis and gives rise immediately 

 to gametes. 



Sporophyte, the spore-producing diploid in the higher plants {v. Gametophy te) . 



Structural Change, change in the genetic structure of the chromosome. May 

 be intra-radial or extra-radial with respect to arms, internal, fraternal 

 or external with regard to chromosomes, symmetrical or asymmetrical 

 with respect to the possession of a centromere, eucentric or dyscentric 

 with respect to the direction of a segment in relation to the centromere. 

 D., 1929 {cf. Ch. XII). 



Secondary , change in structure resulting from crossing-over 



between two homologous segments in chromosomes which are structurally 

 different on both sides of these segments. D., 1932. {Cf. Illegitimate 

 crossing-over.) 



Structure, the potentially permanent linear order of the particles, chromomeres 

 or genes in the chromosomes. Cf. " Structural hybrid." D., 1929 c. 



Subsexual reproduction, parthenogenesis following ameiosis with non-reduction, 

 but with segregation owing to crossing-over. 



[Synapsis], (i) chromosome pairing at zygotene, also described as syndesis ; 

 (ii) contraction of the chromosomes to one side of the nucleus at this 

 stage or at diplotene (an artefact), also described as synizesis. 



Syndiploidy, the fusion of nuclei to give a doubled chromosome number, 

 especially in the divisions immediately preceding meiosis. Strasburger, 

 1907. 



[Syngamy], fusion of gametes. 



Telophase, the last stage of mitosis, after movement of the chromosomes has 

 ceased. Heidenhain, 1894. 



Terminal Affinity, the property by which chromosomes are held together end 

 to end from diplotene till metaphase or brought together in this way at 

 metaphase. D., 1932. 



Terminal Chiasma {v. Chiasma.) 



Terminalisation, expansion of the association of the two pairs of chromatids 

 on one side of a chiasma at the expense of that on the other side. So 

 called because the resulting " movement " of the chiasma is usually if 

 not always towards the ends of chromosomes. D., 1929 c. 



Arrest of , stoppage of the movement of a chiasma through the 



opposite segments distal to it being non-homologous [v. Text). 



Tetrad, (i) quartet of cells formed by meiosis in a mother-cell ; [(ii)] the four 

 chromatids making up a bivalent at meiosis [v. Dyad, Hexad). Nemec, 

 1910. 



Tetraploid, an organism having four sets of chromosomes {v. Polyploid). 

 Nemec, 1910. 



Tetrasomic, an organism with four chromosomes of one type, usually other- 

 wise a diploid [zx -\- 2). 



Torsion-pairing, non-homologous association at pachytene which releases a 

 torsion without satisfying an attraction. D., 1935 c. 



