THr: (iHKAT WELW RACE 



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Mendel's garden peas, in which three alternative pairs of characters are 

 selected, namely, yellow (Y) and green (y) peas; tall (7') and dwarf 

 (0 vines; and axial (A) and terminal (a) flowers. The trihybrids in 

 this case will have the genotypic formula YyTtAa, and will be pheno- 

 typically yellow, tall, and axial. Such hybrids, because of the inde- 



GENOTYPES 



PHENOTYPES 



27 VTA (yellow, tall, axial) 



9 YTa (yellow, tall, terminal) 



9 YtA (yellow, dwarf, axial) 



3 Yta (yellow, dwarf, terminal) 



9 yTA (green, tall, axial) 



3 yTa (green, tall, terminal) 



3 ytA (green, dwarf, axial) 



1 2fta (green, dwarf, terminal) 



64 



Kinds of trihybrids 



pendent assortment of their characters, can produce eight possible 

 kinds of gametes, or mature germ cells, each carrying three charac- 

 ters, as follows: YTA, YTa, YtA, Yta, yTA, yTa, ytA, yta. When 

 these triple gametes unite, there are sixty-four (8 X 8) possible com- 

 binations, as shown in the accompanying checkerboard, which will 

 fall into eight different phenotypic groups in the ratio of 27 : 9 : 9 : 3 : 

 9:3:3: 1 (total 64), and they may be further classified into twenty- 

 seven genotypically different groups, represented above as three 

 monohybrid ratios combined. 



