176 



MULTIPLE FACTORS 



as one of two similar dominant factors producing a 

 non-cumulative result. (Here, then, the 9AB re- 

 semble the 3aB and 3Ab individuals and a 15:1 ratio 

 results.) To those who reject the idea that domi- 

 nance imphes presence, recessiveness absence, there 

 is no great distinction between this case and that of 



9 

 1 



a- 



cD — 



td- 



Cf-*CD 



CD . CD 



I :o 



CJ . CD 



I : 



D . CD 



I : 



:d . CD 



15 : I 



CJ 



1 



CD . CJ 



I : 



CJ . CJ 



I : 



D . CJ 



15 : I 



cJ .CJ 



3 : I 



CD . cD 



I : 



CJ . cD 



15 : I 



cD . cD 



m 



I : 



cJ . cD 



3 :/ 



CD- cJ 



15:1 



CJ . cJ 



3 : I 



cD . cJ 



3 : I 



:d .c4 



: I 



Fig. 54. — Diagram showing the kinds and composition of the F2 capsules 

 of Bursa bursa-pastoris. (After ShuU.) 



the two whites with a 9 :7 ratio. Shull found that 

 when a plant of Bursa bursa-pastoris with round 

 capsules is crossed to one with triangular capsules, 

 the round is recessive to triangular in Fi. In F2 the 

 round reappears only once in sixteen times (Fig. 54). 

 Thus in this cross round may be treated as the result- 

 ant of the two recessive factors, either of which by 



