MendeW Law 



55 



Problems dealing with determiners for which dominance is 

 lacking differ from those where dominance is present only in so 

 far as the monohybrid ratios must differ. 



Cross 



Dominance present 

 Red White 



Phenotypic ratio 



Dominance lackinR 

 (Here phenotypic and gcno- 

 typic ratios are the same) 



Red Pink White 



RRXRR I 



RRXRr I 



RRXrr i 



Rr Xrr 3 



Rr Xrr i 



rr Xrr o 



o 

 o 

 o 

 I 



I 

 I 



I 

 I 

 o 

 I 

 o 

 o 



o 

 I 

 I 



2 

 I 



o 



o 

 o 

 o 

 I 

 I 

 I. 



For example, take the following case, where dominance is pres- 

 ent for the height character and absent for the color character: 



TtRrXttRr. 



The monohybrid ratio as regards height is i talhi dwarf, while 

 the color ratio is i red 12 pinkii white. Multiplying these 

 together gives the dihybrid result, i tall, red:i dwarf, red: 2 tall, 

 pink: 2 dwarf, pink: i tall, white: i dwarf, w^hite. 



LITERATURE CITED 



1. CoRRENS, C, Die neuen Vererbungsgesetze. Berlin. 191 2. 



2. JoHANNSEN, W., Elemente der exakten Erblichkeitslehre. 



Jena. 1909. 



3. Mendel, G., Versuche iibcr Pflanzen-Hybriden. \'erh. Naturf. 



Vereins in Briinn. 4:1865. 



