130 



The J(nirnal of Heredity 



therefore should ^^ivc a 3:1 ratio wiiich When <j;ro\vn in the open, however, the 



can readily be demonstrated in boxes differences are not so readily recoj^- 



in the laboratory. When j^rown in the nized. 



greenhouse, it has been found ])Ossible There is an unarmed race (var. 



to distin<juish heterozygous from homo- incrmis) with smooth capsules. The 



zygous ])urple ]jlants by differences in smoothness of the capsules acts as a 



the intensity of coloration in the flowers, recessive to the spiny character in the 



T.VBLE II 

 (a) Dihyhrid Crosses — Fj Offspring. Expcclcd Ratio — 9 :3 :3 : 1 



(6) Dihybrid Crosses — Fi X Double Recessive. Expected Ratio — 1 : 1 : 1 : 1 



Parentage 



Purple 

 armed 



Purple 

 inermis 



White 

 armed 



White 

 inermis 



Plants heterozygous for both purple j 

 and spines, crossed with plants j Recorded 

 recessive for both of these char- 



89 



86 



99 



88 



acters. 

 Genetic formula — PpAaXppaa 



Expected 90 . 5 



90.5 



90.5 



90.5 



(c) Monohybrid Crosses* — F2 OfFspriii}^. ExiJceted Ratio — 3 : 1 



Purple White Armed 



Parentage 



Inrniiis 



Plants heterozygous for purple, Recorded 



either selfed or intercrossed. ! 



Genetic formula — PpXPp | Expected 



2606 



914 



2640 



880 



Plants heterozygous for spines, 

 cither selfed or intercrossed. 

 Genetic formula — AaXAa 



Recorded 



987 



Expected 



985.5 



327 



328.5 



(d) Monohybrid Crosses* — FiXRecessive. Expected Ratio — 1 : 1 



' There are included here the records for stem and spine characters abstracted from the 

 dihybrid summaries given in the table above. 



