APPENDIX I 



Coupling, the presence of two given genes in tlic same chromosome in 

 a double lictcrozygote, as opposed to Repulsion, where they are 

 in different homologous chromosomes. Bateson, Saunders and Punnett 

 1906. 



CovARiANCE, the mean of the products of corresponding deviation of 

 two variates from their individual means. Estimated as the ratio of 

 the sum of Cross Products to the corresponding number of Degrees 

 of Freedom. 



Criss-Cross Inheritance, v. Inheritance. 



Cross, an act or product of cross fertilization. 



Crossbreeding, Outbreeding, v. Inbreeding. 



Cross-Fertilization (Crossing), v. Fertihzation. 



Cross Products, Sum of, sum of the products of corresponding 

 deviations of two variates from their individual means. 



Cross Sterility, v. Sterility. 



Crossing-over, the exchange of corresponding segments between 

 chromatids of homologous chromosomes, by breakage and reunion 

 following pairing; a process inferred, genetically, from the recom- 

 bination of linked factors in the progeny of heterozygotes, and, 

 cytologically, from the formation of chiasmata between homologous 

 chromosomes. Morgan 191 1. 

 Crossing-over Value, the frequency of crossing-over between two 

 genes or markers. Often loosely used for Recombination Value to 

 which it may however be equated when small. 

 Double Crossing-over, the production of a chromatid in which 

 crossing-over has occurred twice (for further classification 

 V. Chiasma). Sturtevant 1914. 

 Effective Crossing-over, that wliich is detectable in breeding experi- 

 ments. Darlington 1937. 

 Illegitimate Crossing-over, crossing-over, in a haploid or polyploid 

 which is not a structural hybrid, between homologous and reduph- 

 cated segments of two chromosomes, wliich, being structurally 

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

 Structural Change. Darlington 1932. 

 Somatic Crossing-over, crossing-over at mitosis as opposed to meiosis 



(either in somatic or germinal tissue). Stern 1935. 

 Unequal Crossing-over, such as produces one chromatid containing 

 a gene twice and another lacking that gene. Due to inaccurate 

 pairing, e.g. of the Bar gene in Drosophila nielanogaster. 



Cumulative Factors, v. Polymeric Genes. Nilsson-Ehle 191 1. 



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