PHENOMENA OF INHERITANCE 243 



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 (W) and green (G) 

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

 the FI generation have round and yellow seeds 

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

 to W, G, and D. But 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 



