Knight — 24 — Dictionary 



Cervix (uteri). — The neck of the uterus leading into the 

 vagina. 



Cevitamic Acid. Vitamin C, 



Character, Characteristic. — The phenotypic result of the 

 interaction of a gene or group of genes and the environment. 



Character Gradients. — Clines, q.v. 



Character-unit. — An obsolete synonym for gene. 



Chasmogamy. — The opening of the perianth at the time of 

 flowering, as opposed to cleistogamy. Adj. Chasmogamic. 



Check Cross. — A cross of an individual of unknown geno- 

 type with a phenotypically similar individual of known geno- 

 type in order to determine, in Fg, whether the same gene or 

 allelic series is responsible for the phenotypic appearance of 

 both individuals. 



Chemo-differentiation. — The initial stage of cell differen- 

 tiation in which cytoplasmic chemical changes occur unac- 

 companied by any visible change in the cells. 



Chi. — See Appendix 1. 



Chiasma-ta. — An exchange of partners in a system of paired 

 chromatids ; observed between diplotene and the beginning of 

 the first anaphase in meiosis (Janssens; Darlington). A 

 visible change of pairing affecting two out of the four chro- 

 matids in a bivalent at meiosis; an outward sign that a gene- 

 tical cross-over has taken place (White). See also under 



Comparate , Complementary , Disparate , Distal 



, Inversion , Proximal , Reciprocal , Sym- 

 metrical . 



Compensating . Where one chiasma restores the 



association interrupted by the other (Newton & Darling- 

 ton). 



Imperfect . Where one of the four associations in a 



chiasma is broken prior to anaphase (Darlington). 



Interstitial . Where there is a length of chromatid 



on both sides of the chiasma (Darlington). 



Lateral . A chiasma which is terminal as to two 



chromatids and interstitial as to the others. Of two kinds, 

 symmetrical and asymmetrical (Darlington). 



Multiple . A terminal chiasma where three or four 



pairs of chromatids are engaged (Darlington). 



Terminal . Those which occur at the extremities of 



the chromatids. 

 Chiasma Frequency. — The average number of chiasmata 

 formed per bivalent, or in any particular bivalent, in a given 

 organism under given circumstances. 



