4 



Mr. W. Bateson and Prof. K. C. Punnett. [Mar. 2, 



The partial coupling was next shown to be approximately in case (1) 

 7BL : 1B1 : lbL : 7bl, 

 where B is blue and L is long pollen ;* 

 and in case (2) to be 



15DF : lDf : ldF : 15df, 



where D is dark axil and F is fertile anthers. 



(4) At this stage, investigation of the properties of the exceptional members 

 of the F 2 series was begun. In particular, the combination dark axil with 

 sterile anthers (Df) was crossed with a light-axilled plant having normal 

 anthers (dF). The F 2 generation from this cross was, to our surprise, a 

 series in which all the sterile plants had dark axils. Here, therefore, there 

 had been a repulsion between the same two factors which had been coupled 

 in case (2). 



In considering what could have determined this difference in behaviour, it 

 seemed possible that the distinction might have been due to the way in 

 which the factors had been combined in the original parents, for we knew 

 that in the cases where coupling had resulted, the two dominant factors had 

 been introduced together from the same parent, whereas in this new case one 

 had come from each parent. 



For several years this conjecture has been made the subject of elaborate 

 tests, and its correctness has now been completely substantiated in several 

 examples. Expressed in a general form, the conclusion to which we have 

 been led is that if A, a, and B, b, are two allelomorphic pairs subject to 

 coupling and repulsion, the factors A and B will repel each other in the 

 gametogenesis of the double heterozygote resulting from the union 

 Ab x aB, 



but will be coupled in the gametogenesis of the double heterozygote resulting 

 from the union 



AB x ab. 



The Fi heterozygote is ostensibly identical in the two eases, but its 

 offspring reveals the distinction. We have as yet no probable surmise 

 to offer as to the essential nature of this distinction, and all that can yet be 

 said is that in these special cases the distribution of the characters in the 

 heterozygote is affected by the distribution in the original pure parents. 



In F 2 , from a system in which A and B are coupled, almost all the 

 offspring in the form AaBb will be again built up from AB and ab gametes, 



* There are indications that this distribution may be liable to disturbance by other 

 factors in a way not yet understood (' Reports Evol. Committee,' IV, pp. 11 — 13). 



