Mechanism of Mendelian Heredity 235 



are ready for the production of a new individual, each 

 loses one set of homologous chromosomes in the so- 

 called reduction division, but the lost set is made up 

 indiscriminately of maternal as well as paternal chro- 

 mosomes, so that while one egg retains the maternal 

 chromosome A the other will retain the paternal one, 

 and so on. If before the reduction division all the eggs 

 had the chromosome constitution A A x , BB lt CC^ DD^ 

 (where A B C D are the paternal and A z Bj. C x D^ the 

 maternal chromosomes), after the reduction division 

 each daughter cell has a full set of four chromosomes, 

 but maternal and paternal mixed. Thus the one cell 

 may have AB^CD^ the other A^S^dD, etc. This, 

 according to Button, is the basis of the Mendelian 

 heredity. Suppose the determiner of a certain char- 

 acter (violet colour of flower in the bean) is located 

 in a chromosome A of this species. The homologous 

 chromosome in beans with white colour may be desig- 

 nated as a. According to the chromosome theory of 

 Mendelian heredity a differs from A in one point, 

 though this difference is probably only of a chemical 

 character and not visible. 



If an egg with A is fertilized by a pollen with a 

 (or vice versa), after fertilization the chromosome con- 

 stitution of the fertilized egg is A a. All the other 

 homologous chromosomes are identical and therefore 

 need not be considered. All the nuclei of the F r 

 generation have the chromosome constitution A a. 



