236 Mechanism of Mendelian Heredity 



All will form eggs and pollen with nuclei of the same 

 chromosome constitution Aa, but all these sex cells 

 will go through the maturation division before they are 

 fertilized; and this reduction division leads to the 

 existence of two kinds of eggs in equal numbers, one 

 containing only the A, the other only the a chromosome; 

 and the same happens in the pollen. When therefore 

 the hybrids F x are mated among themselves, the 

 following four chromosome combinations will be pro- 

 duced: 



Eggs Pollen Possible combinations in fer- 



A a A a tilized eggs A A, Aa, aa, in 



I ~ Id^^^^"^-^ I the ratio 1:2:1. 

 I r ^.^"^-z^c^'^ 



Now this is exactly the ratio of Mendelian heredity 

 in the F 2 generation. The plant with the chromosome 

 constitution A A will form violet flowers, those with the 

 chromosome constitution A a will form pale violet 

 flowers, and those with the chromosome constitution 

 aa will form white flowers. 



To quote Button's words: 



The result would be expressed by the formula AA: Aa: 

 aa which is the same as that given for any character in a 

 Mendelian case. Thus the phenomena of germ cell divi- 

 sion and of heredity are seen to have the same essential 

 features viz., purity of units (chromosomes, characters) 

 and the independent transmission of the same; while as a 

 corollary it follows in each case that each of the two antago- 



