HEREDITY AND VARIATION 





allelomorphs. 



If the genes involved be represented as follows : 



A =gene for Crimson flower colour | 



a= „ Ivory ,, ,, J 



B = ,, Normal flower form ^ „ . 



b= „ Peloric „ „ } ^^'""^Phs. 



then the genotype of the Ivory Normal parent is aaBB, that of the ( rm 

 Peloric parent AAhb. If these genes segregate Independently their i 

 gametes will be aB and Ab, and the genotype of the F, AaBb. A plant of this 

 constitution will produce four different kinds of gametes, viz. AB, Ab. aB, and 

 ab, in equal numbers. Random mating between these can take place m 

 teen different ways. The simplest method of showing the results is by m< 

 of a " chequerboard " (Fig. 439). 



Fig. 439. r. 1 • 



"Dihvbrid" Segregation. Cross between an Ivory, Normal and a Cnmson. l« 

 Snapdragon. Chequerboard showing the segregation in the P, generation in detail. 



If it is borne in mind that : 



Every individual with a double "dose " of A will be Crimson. 



„ „ single dose of A will be Pink. 

 La< kino a will t> 1 \ »ry. 



with a double or a single dose ol B will rmaL 



lacking B will be Peloric. 



