574 APPENDIX III 



Chiasma Theory of Pairing, the hypothesis that whenever two chromosomes 

 which have been paired at pachytene remain associated until metaphase 

 they do so by virtue of the formation of a chiasma or visible exchange of 

 partners amongst their chromatids. D , 1929, h and c. 

 Chiasmatype Theory, (i) the theory that chiasmata are connected with 

 crossing-over either as a cause or as a consequence. Janssens, 1909. 

 (ii) The special assumption that chiasmata are determined by crossing- 

 over between two non-sister chromatids of the four involved. D., 

 19306. 

 Chimaera, a plant composed of tissues of two genetically distinct types as a 

 result of mutation, segregation, irregularity of mitosis, or artificial fusion 

 (graft-hybrids), v. Mosaic. Cf. Baur, Winkler. 

 Chondriosomes, bodies in the cytoplasm which are believed to be self- 

 propagating, including mitochondria and Golgi-bodies. Benda, 1904. 

 Chromatid, a half chromosome between early prophase and metaphase of 

 mitosis and between diplotene and the second metaphase in meiosis — ■ 

 after which stages, i.e., during an anaphase, it is known as a daughter- 

 chromosome. The separating chromosomes at the first anaphase are 

 known as daughter-bivalents, or, if single chromatids derived from the 

 division of univalents, daughter-univalents. McClung, 1900. 



Non-Disjunction, the passing of homologous parts of chromatids 



to the same pole following crossing-over between homologous differential 

 segments in a multiple interchange hybrid. E. Sansome, 1933. 



bridge, dicentric chromatid with centromeres passing to opposite 



poles at anaphase. 



Sister s, those derived from division of one and the same chromo- 

 some, as opposed to non-sister chromatids which are derived from 

 partner chromosomes at pachytene. 

 Chromatin, the part of the chromosome that stains deeply during mitosis, as 

 opposed to an achromatic part. The distinction is difficult to apply and 

 is often of doubtful validity. Flemming, 1879. 

 Chromocentre, (i) fused prochromosomes (q.v.) ; (ii) body produced by fusion 

 of the centromeres, etc., in nuclei of the salivary glands of certain Diptera. 

 Painter, 1935. 

 Chromomeres, the smallest particles identifiable by their characteristic size 

 and position in the chromosome thread between leptotene and pachytene 

 and in salivary gland nuclei. Wilson, 1896. 

 [Chromonema, -ta], the chromosome thread, q.v. (similarly leptonema, 

 pachynema, etc., the chromosome threads at leptotene, pachytene, etc.). 

 Wilson, 1896. 

 Chromosomes, one of the bodies into which the nucleus resolves itself at the 

 beginning of mitosis and from which it is derived at the end of the mitosis. 

 Waldeyer, 1888. 



Acentric , one lacking a centromere. 



Dicentric , one with two centromeres. 



Ring , one with no ends. 



Chromosome Thread, the thread consisting of centromere, chromomeres, 

 achromatic connective thread and, perhaps, pellicle at prophase ; and 

 constituting, as a spiral, the metaphase chromosome. 

 Clone, a group of organisms descended by mitosis from a common ancestor. 

 Coil, V. spiral. 

 Complement, the group of chromosomes derived from a particular nucleus in 



gamete or zygote, composed of one, two or more sets (q-v.). 

 Condensation or Contraction of the chromosome, the thickening, shortening 

 and spiralisation of the chromatids during prophase {v. Text). 



