Knight — 34 — Dictionary 



Crisscross Inheritance. — The scheme of inheritance whereby 

 the female is normally the heterozygous carrier of a recessive 

 sex -linked gene the effect of which is only evident in her sons. 



Criss-crossing. — The continuous use of pure bred sires on 

 alternate breeds. "Thus sows produced by crossing breeds A 

 and B would be mated back to A. Their daughters . . . would 

 be mated to a B boar. The gilts thus produced . . . would then 

 be mated to an A boar" (Lush, 1943). 



Cross. — N. A hybrid; an individual whose parents differed 

 genetically. V. To hybridize. 



Cross Homology. — Residual homology, q.v. 



Cross-incompatibility. — The inability of the gametes from 

 two different individuals to unite although the individuals 

 themselves are otherwise fertile. 



Crossing-over. — An exchange of corresponding segments be- 

 tween the chromatids of homologous chromosomes. 



Double . — The production of a chromosome in which 



crossing-over has occurred twice; may be reciprocal or non- 

 reciprocal as between chromatids at meiosis (Sturtevant; 

 Darlington). 



Effective . — Crossing-over which is demonstrable by 



means of progeny tests. 



Illegitimate . — Crossing-over in a haploid or poly- 

 ploid which is not a structural hybrid, between homologous and 

 reduplicated segments of two chromosomes which, being struc- 

 turally dissimilar as a whole, do not normally pair. Determines 

 secondary structural change (Darlington). A physical ex- 

 change between non-homologous chromosomes or between 

 non-corresponding segments of a single chromosome. 



Somatic . — An exchange of segments between ho- 

 mologous chromosomes at mitosis. 



Crossover Region. — The segment of a chromosome which 

 lies between any two specified gene loci. 



Cross-over Suppressor. — Any gene inhibiting crossing-over. 



Cross-over Unit. — A cross-over value (q.v.) of 1%. 



Cross-over Value. — The sum of the two recombination classes 

 in a backcross expressed as a percentage of the total offspring. 



Cross-pollination. — The act of placing on the stigma of a 

 flower, pollen derived from another plant not in the same 

 clone. 



Cryptic Coloration. — Coloration which camouflages the in- 

 dividual so that it is less readily seen. 



Cryptic Contamination. — Contamination of a seed supply by 

 outcrossing, the contamination not being evident in the ira- 



