HEREDITY 



329 



are twenty-four synaptic pairs of chromosomes, with a probably 

 very great number of pairs of allelomorphic genes. If we were to 



PARENTS- 



TALL YELLOW SMOOTH 

 TT YY SS 



DWARF GREEN WRINKLED 



TT YY SS 



Tt Yr Ss 



GERM CELLS OF ^! 



EGGS 



S 

 P 



i< 



M 



TYPES 

 OF 



PROGENY 



GENER- 

 ATION 



Fig. 206. — ^The segregation of genes in a trihybrid cross In peas: Tall (T) and its 

 alternative Dwarf (/); Yellow seed color (Y) and its alternative Green (y); Smooth 

 seed coat (5) and its alternative Wrinkled {s). 



consider the probabiHty of occurrence of a triple recessive in a hu- 

 man cross involving three pairs of characters, Fig. 205 indicates 

 that it will occur but once in sixty-four chances. Since the number 



