HERITAGE OF THE INDIVIDUAL 



281 



SYR 



ayr 



SYR sYR SyR syR SYr 



sYr 



Syr 



syr 



SYR 



sYR 



SyR 



syR 



SYr 



Syr 



syr 



FIQ. 143. Diagram of a Mendelian trihybrid. Results of crossing tall Peas bearing 

 yellow round seeds (SYR) with dwarf Peas bearing green wrinkled seeds (syr). The 

 circles represent the zygotes and the characters of the soma (phenotype) ; the letters 

 within the circles, the germinal constitution (genotype). The letter groups outside the 

 recombination square represent the gametes. The Fi hybrids form eight types of game- 

 tes, giving sixty-four possible types of zygotes, representing eight phenotypes (shown 

 graphically) and twenty-seven genotypes. There is one pure (extracted) dominant 

 (upper left corner) and one recessive (lower right corner). Eight are homozygotes 

 (diagonal from upper left to lower right corner) and the rest are heterozygotes. The 

 zygotes in the diagonal from upper right to lower left are identical with the Fi generation. 

 The relative number of individuals composing the phenotypes is 27 : 9 : 9 : 9 : 3 : 3 : 3: 1. 



