22)2 Mechanism of Mendelian Heredity 



(2) violet — white; (3) violet — white; (4) white — white. 

 The first will result in pure violet flowers, the fourth 

 in pure white, and the second and third in pale violet 

 flowers. Since all four combinations will appear in 

 equal numbers when the number of crossings is suffi- 

 ciently large the numerical result will be: 



violet : pale violet : white =1:2:1 



Fifty per cent, of the F2 generation will be pale 

 violet, 25 per cent, violet, and 25 per cent, white. The 

 violets and whites each will breed true when bred 

 among themselves since they are pure, and produce 

 only one type of eggs and pollen. The pale violets 

 are hybrids and will again produce the two types 

 of eggs and pollen, that is, if bred among themselves 

 will again give violets, pale violets, and whites in the 

 ratio 1:2: I . This the experiment confirms. 



As has been stated, it not infrequently happens that 

 all the hybrids of the first generation are alike. In such 

 cases the one character is "recessive, " i.e., overshadowed 

 or covered by the other the "dominant" character, 

 which alone appears in the hybrids. Thus when 

 Mendel crossed peas having round seeds with peas 

 having angular seeds all the hybrids had round seeds. 

 The round form is dominant, the angular recessive, 

 i. e., all the hybrids have round seeds. When these 

 hybrids were bred among themselves the next genera- 



