Heredity and Environment 

 WGD 



F, 



RYT RYD RGT ROD WYT WYD WGT WGD 



FIG. 32. TRIHYBRID DIAGRAM SHOWING RESULTS OF CROSSING PEAS HAV- 

 ING ROUND YELLOW SEEDS AND TALL STEM (RYT) WITH PEAS HAVING 

 WRINKLED GREEN SEEDS AND DWARF STEM (WGD). Eight types of germ 

 cells are formed by the F 1 hybrid, as shown in the $ gametes above the 

 square and the $ ones to the left of it, and the possible combinations 

 of these $ and $ gametes are shown in the 64 small squares of which 

 only I is pure dominant (upper left corner), I pure recessive (lower' 

 right corner) and 8 homozygotes (in diagonal line between these corners). 

 There are 27 different genotypes, all combinations below this diagonal be- 

 ing homologous with the corresponding ones above and all in the other 

 diagonal being of the same genotype, while 12 other combinations on 

 each side of the first diagonal constitute only 6 genotypes. There are 8 

 phenotypes, resembling the 8 homozygotes, and their relative numbers 

 are 27 RYT : 9 RYD: 9 RGT \ 9 IVY T : 3 ROD : 3 WYD -.3 WGT: i WGD. 



