12 



Segregation 



[CH. 



DD x RR gives 

 DRxRR gives 

 DR^DD gives 

 x DR gives 



v\\DR 



iRR 



: iRR 



appearing as 3 dominants : i recessive. 



The way in which these ratios are produced may be 

 easily represented by means of a number of draught-men. 

 Pairs of draughts then represent zygotes ; single draughts 

 represent germ-cells. That there is a propriety in repre- 

 senting zygotic or somatic cells as double structures and 

 germ-cells as single structures will be evident to biologists ; 

 for we know that each somatic nucleus in plants and 

 animals is a double structure, containing twice the number 

 of chromosomes present in each mature germ-cell. Two 

 black draughts may then be taken to represent a pure black 

 individual, two white draughts a white individual. When 

 they are crossed together F^ is represented by a black 



