MKkKIHTY AND VARIATK 





Snapdragon, the F 2 generation t h u- comprises three visibly distini t forms or 

 pheuotvpcs. In the Pea, on the contrary, where taHne 



over dwarfness, the " pure tails " and the " hybrid tails " arc pfa illy 



identical; their different behaviour after being fed," bo* 



that they have different genetic constitutions, i.e. that they re] 

 genotypes. 



Fig. 437. 



"Mono-hybrid" Segregation. Cross between ia crimap q faa^m 



black) and an ivory Snapdragon (shown white). I be offe] 

 grey) The F 2 generation produced by self-fertilising an F, indivulu 

 crimson-, pink- and ivory- flowered plants, in the proportion indicated m 0* 

 (From Shull's Heredity by courtesy of the McGraw-Hill Book Co., Incj 



(6) Involving Two Pairs of Charade) , 

 A " dihybrid " cross is one between two individuals differing in two in- 

 dependently segregating Mendelian characters; ral men 

 examined and explained by Mendel in t! . As our first example we BhaU 

 consider the cross between an " ivory " Snapdragon with normal flowers and 

 a crimson Snapdragon with " peloric " flowers (Fig. 4 3») i " *Ottld 

 plained that, whereas the normal form of tin- flower in Snapdra( 

 morphic, races exist in which all the flowers are actinomorphie (" | 

 and thus quite unlike the usual type in appearance. From what has K-. n 



B.B. 2 



