1911.] On the Inter-relations of Genetic Factors. 



5 



so that they will again exhibit coupling ; but a very small proportion will be 

 formed from the comparatively rare gametes aB and Ab. Such heterozygotes 

 will probably show repulsion in their gametogenesis. They must, however, 

 be so rare (only 2 in 256, for example, from the system 7AB : laB : lAb : 

 7ab ) that it is almost hopeless to look for them in practice. 



We know, moreover, that these phenomena are not peculiar to the sweet 

 pea, but that they must exemplify widespread principles of genetic physiology. 

 Kepulsion has been found between the factor for femaleness and several 

 factors of various kinds in animals — e.g., in Abraxas grossulariata ; in the 

 canary ; in the fowl for at least three factors — i.e. (1) the factor which 

 inhibits the development of the peculiar mesoblastic pigment of the Silky, 

 (2) the dominant " silver " of Assendelvers (Hagedoorn) and of Sebrights 

 (ourselves, unpublished), (3) the barring factor of Plymouth Kocks (Spillman ; 

 Pearl). Coupling till recently had been observed in the sweet pea only. 

 Now we have the additional examples published simultaneously with this 

 note, namely, tendrils and round seed in Pisum (de Vilmorin and Bateson), 

 and short style and magenta colour in Primula sinensis (Gregory). In 

 addition to these cases of coupling, Gregory also contributes a new example 

 of repulsion, between green stigma and the factor which diminishes the 

 stem-colour. There is thus good reason to believe that these phenomena are 

 of no restricted occurrence in nature. 



In work already published we have shown that coupling occurs according 

 to the systems 



7AB : laB : lAb : 7 ab 

 and 15AB : laB : lAb : 15ab. 



Such systems pointed to the existence of others which could be given by 

 the expression 



3n 2 -(2n-l) : 2n-l : 2n-l : n 2 -(2n-l), 

 where n is half the number of gametes needed to express the whole system. 



Two more of the systems thus contemplated as possibilities have been 

 discovered. The cases now stand thus : — 

 3:1. No case yet known. 

 7:1. Sweet Pea. Blue factor and long pollen. 

 7:1. Primula sinensis. Magenta colour and short style. 

 15 : 1. Sweet Pea. Fertile anthers and dark axils. 

 31 : 1. No case yet known. 



63 : 1. Pisum. Development of tendrils and round seed. 

 127 : 1. Sweet Pea. Blue factor and erect standard. 



For all of these except the Pisum case (as yet untried) repulsion is also 



