GLOSSARY 573 



Apospory, apomixis involving the replacement of the spores by unspecialised 

 cells which have not undergone meiosis. Bower, 1887 ; cf. Winkler, 1908 ; 

 Rosenberg, 1930. 



Asynapsis, non-pairing of chromosomes at meiosis. Beadle, 1931. 



Attachment, [(i) the position of the centromere, 5'. y. ;] (ii) the permanent fusion 

 of two chromosomes. L. V. Morgan, 1922. 



Autosomes, those chromosomes whose segregation does not normally affect 

 the determination of sex (as opposed to sex-chromosomes). Mont- 

 gomery, 1906. 



Autosyndesis, the pairing, in a polyploid, of chromosomes derived from the 

 same parent ; particularly its exceptional occurrence in an allopoly- 

 ploid or its hybrid. Ljungdahl, 1922. 



Azygote, organism arising by haploid parthenogenesis. Whiting and Benkert, 



1934- 

 Balance, the condition in which the genes are adjusted in proportions which 



give satisfactory and normal development of the organism (opposite : 



unbalance). Bridges, 1922. 



Secondary , a new balance derived by change in the proportion of 



genes, as in a secondary polyploid, from an old balance, and capable of 



competing with it. D. and Moffett, 1930. 

 Balanced Lethal Factors, v. Lethal. 

 Basic Number. The supposed number of chromosomes found in the gametes 



of a diploid ancestor of a polyploid, represented by x. 

 Bivalent {v. Univalent). 

 Bouquet, the zygotene and pachytene stage in those organisms in which the 



chromosomes lie in loops with their ends near one part of the wall of the 



nucleus {cf. Polarisation) . Eisen, 1900. 

 Cell, a unit in the structure of the animal or plant containing one nucleus, or 



several where these are separated by a uniform substratum. Also a body 



derived from such a unit. Leeuwenhoek, Schleiden and Schwann, 1840. 

 Centromere, a particle in the chromosome thread w^hose special cycles of 



repulsion and division determine the anaphase and terminalisation 



movements of the chromosomes [v. Table 75). 

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



organisms lies at the two poles of the spindle and appears to determine 



its orientation. Boveri, 1885. 

 Chiasma, -ta (Hellenistic Greek), an exchange of partners in a system of paired 



chromatids ; observed between diplotene and the beginning of the first 



anaphase in meiosis. Janssens, 1909. 



Comparate and disparate ta, pairs of successive chiasmata which 



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



regard to the crossing-over and changes of partner producing them. 

 Interstitial , where there is a length of chromatid on both sides 



of the chiasma. D., 1929 c. 



Reciprocal and Complementary ta, the tw^o kinds of comparate 



chiasmata according to their crossing-over relationships. 



Terminal , where an exchange occurs amongst the end particles 



of the chromatids, following terminalisation. D., 1929 c. 



Multiple , a terminal chiasma where three or four pairs of 



chromatids are engaged. D., igzg c. 



Lateral , a chiasma which is terminal as to two chromatids and 



interstitial as to the others. Of two kinds, symmetrical and asymmetrical . 



D., 1929 c. 



Imperfect , where one of the four associations in a chiasma is 



broken prior to anaphase. D., 1929 c. 



