224 



Inheritance in Doliclios lablab, L. 



Interpretation of the Experimental Results. 



1. Two factors are concerned in the production of the purple colour 

 of the flower. These may bo denoted by the symbols C and R, while 

 their allelomorphs may be represented by c and r. 



2. In the presence of both factors the flower is purple. In the 

 absence of either the flower is white. 



3. According to this view the cross is of the nature cR x Cv 

 (St Vincent Bush x Vilmorin's Stringless). The genotypes appearing 

 in Fo will be as follows : 



Homozygous 



Heterozygous 



Genotype 



CRCR 

 CrCr 

 cRcR 

 crcp 



No. 



1 

 1 

 1 

 1 



Colour 



Purple 

 White 

 White 

 White 



Genotype 



CRCr 



CRcR 



CRcp 



Cpcp 



cRcP 



No. 

 2 

 2 

 4 

 2 

 2 



Colour 



Purple 

 Purple 

 Purple 

 White 

 White 



Behaviour in F^ 



3p : lie 



3p : Iw 



9p :7w 

 All white 

 All white 



The ratio of purple to white in i'^ is 9 : 7. In F^ of the 9 purples 1 

 will breed true ; of the remaining 8 purples 4 will segregate into purple 

 and white in the 9 : 7 ratio, and 4 into purple and white in the 3 : 1 

 ratio. The ratio between the three kinds of families is thus 1:4:4. Of 

 the 7 whites, all will breed true. In F^ the purples from F^ families 

 which produced the 3-1 type of ratio, will again produce this type of 

 ratio, or else breed true, and the ratio of pure to heterozygous purples 

 will be 2:1. Purples from F^ families which exhibited the 9 : 7 ratio, 

 will behave in the same way as F^ purples, i.e. ^ will breed true, | will 

 give Sp:lw, and f will give 9 p : 7 w. All Fs whites will remain con- 

 stant in ^4. 



It remains to see how far this hypothesis is confirmed by the experi- 

 mental results. From the latter we see that : 



1. The ratio of purple to white in Fo, is 484 : 342 (9-3 : 6-7), which is 

 near to the expected one of 9 : 7. 



2. The 25 F2 whites which were grown on into Fs, produced only 

 whites. This is in accordance with theory. 



3. Of 65 families from F^ purples, 35 exhibited the 9 : 7 ratio, 25 

 the 3 : 1 ratio, while 5 bred true. The expected numbers are 29, 29, and 

 7 respectively. The actual number of families following the three types 

 of behaviour is thus not far from expectation. 



4. White flowered plants, whether from F2 or F^ families, invariably 

 bred true. 



