PHENOMENA OF INHERITANCE 249 



right corner. All other individuals are heter- 

 ozygous and show Mendelian splitting in the 

 next generation. 



When parents differ in three contrasting 

 characters a much larger number of combina- 

 tions is possible in the F 2 generation. Thus 

 if a pea with round (R) and yellow (Y) 

 seeds, and with tall (T) stem is crossed with 

 one having wrinkled (TV) and green (6r) 

 seeds, and dwarf (D) stem all the progeny of 

 the Fi generation have round and yellow seeds 

 and tall stem, R, Y , and T being dominant 

 over W , G, and D. In the F 2 generation 

 there are sixty-four possible combinations 

 (genotypes) of these six characters; but since 

 a recessive character does not develop if its 

 contrasting dominant character is present there 

 are only eight types which come to expression 

 (phenotypes) and in the following numbers: 

 27RYT : 9RYD : 9RGT : 3RGD : 9WYT 

 : 3WYD : 3WGT : 1WGD. Of these sixty- 

 four genotypes only eight are homozygous and 

 breed true (those lying in the diagonal be- 

 tween upper left and lower right corners in 

 Fig. 54), while only one is pure dominant 



