'250 



HEREDITY AND ENVIRONMENT 



RYT WGD 



VWGDy 



RYT RYD RGT ROD WYT WYD WGT WGD 



Fig. 54. Trihybrid Diagram showing results of crossing 

 peas having round-yellow seeds and tall stem (RYT) with 

 peas having wrinkled-green seeds and dwarf stem (WGD). 

 Eight types of germ cells result from such a hybrid, as shown 

 in the £ gametes above the square and the 5 ones to the 

 left of it, and the possible combinations (genotypes) of 

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

 which only 1 is pure dominant (upper left corner), 1 pure 

 recessive (lower right corner) and 8 homozygotes (in di- 

 agonal line between these corners). The relative numbers 

 of the different phenotypes are 27RYT: 9RYD: 9FX1T: 9 WYT: 

 3RGD: 3WYD: 3WGT: 1WGD. 



