No. 597] INHERIT AXCE STUDIES IX PlsCM 



513 



Crossed with each other these give : 



(lX2)=YYGgli (F x ) yellow, (F,) 13Y:3G 



(lXS^YYGKHifFJ yellow, (F,) 3Y:lGr 



(2x3)=YYGgii (FJ green, (F 2 ) 1Y:30 



The hereditary substances responsible for yellow pig- 

 ment, of course, have not been isolated and may take the 

 form of more than one factor, but I have represented 

 these as Y, to make my interpretation clearer. The essen- 

 tial point in the interpretation is that all the hereditary 

 differences in cotyledon color in Pisum so far discovered 

 may he pictured as due to the presence or absence of tw 

 genetic factors. 



TABLE IV 



Factorial Composition of F 3 Plants of the Three Crosses and the 

 Appearance op the F 3 Progeny 

 Dominant Yellow X 'Recessive Yellow and Reciprocals 



1 YYGGII Breeds true to yellow cotyledons 



9 yell w 2 YYGGIi 3 Y: 1 G 



76 ° W 2 YYGgll Breeds true to yellow but heterozygous for G 



4 YYGgli 13 Y: 3 G 



1 YYGGii Breeds true to green cotyledons 



3 green 



YYGgi: 



3 1 YYggii Breeds true to yellow cotyledons 



3 2 YYggii Breds true to yellow but heterozygous for I 



1 yellow 1 YYggii Breeds true to yellow cotyledons 



Dominant Yellow X Green and Reciprocals 



3 1 YYGGII Breeds °true to yellow cotyledons 



}e ° W 2 YYGGIi 3 Y: 1 G 



1 green 1 YYGGii Breeds true to green cotyledons 



Recessive Yellow X Green and Reciprocals 



1 yellow 1 YYggii Breeds true to yellow cotyledons 



3 1 YYGGii Breeds true to green cotyledons 



green 2 YYGgii 1 Y: 3 G 



Regarded thus, the F 2 plants of all crosses so far made 

 in Pisum, involving cotyledon color, can be represented 

 by the gametic formulae given in Table IV. The char- 



