3 



On the Inter-relations of Genetic Factors. 

 By W. Bateson, F.B.S., and B. C. Punnett, Professor of Biology in the 

 University of Cambridge. 



(Received March 2— Bead March 30, 1911.) 



The nature and bearing of the observations to be recorded in this paper 

 will best be explained by tracing the steps by which they have been 

 reached. 



Early in the investigation of heredity in the sweet pea it was observed 

 that when plants were heterozygous for two separate pairs of allelomorphs 

 the distribution of the factors concerned was in certain cases disturbed in 

 definite ways, such that particular combinations occurred in the gametes with 

 greater frequency than others. 



(1) The first case noticed was that of F x plants heterozygous for blue and 

 red colour, and for long and round pollen. In the F 2 generation all possible 

 combinations were represented, but the blues were for the most part long- 

 pollened and the reds were for the most part round-pollened. 



(2) The next case observed was that of Fi plants heterozygous for dark and 

 light axils on the one hand, and for fertile and sterile anthers on the other. 

 In this F 2 also all combinations occurred, but nearly all the dark-axil plants 

 had fertile anthers, while nearly all the light-axilled plants had sterile 

 anthers. 



(3) The next step was made by a study of the F 2 from plants heterozygous 

 for blue and red flowers and for erect and hooded standards. Here it was 

 found that one of the possible combinations did not exist in F 2 , for though 

 the blues might be either erect or hooded, the reds were all erect. 



Examining these occurrences in the light of the presence-and-absence 

 theory, it was clear that the phenomenon presented by cases (1) and (2) was 

 entirely distinct from that presented by case (3). For whereas in (1) and 

 (2) there was excess of gametes bearing the two factors over those bearing 

 one or the other alone, the condition produced in (3) could only be obtained 

 by a distribution such that no gamete could carry both positive factors. We 

 were therefore led to recognise — 



A. A system of partial coupling under which two factors are generally 

 associated. 



B. A system of complete repulsion (or as we have sometimes called it, 

 " spurious allelomorphism ") under which two factors are never associated in 

 the same gamete. 



b 2 



