1 2 Segregation [CH. 



DD x RR gives all DR 



DR x RR gives iZ^T? : \RR 



DR x Z?Z? gives \DD : iDR 



DR x DR gives iZ?> : zDR : iRR 



appearing as 3 dominants : i recessive. 

 I 



r Rl I mmv HH MH 



2 Rl 1 I IR I IR MVD 



i? IRR : 2DR ' : IDD 



IR 3D 



Fig. a. Diagrams showing numerical consequences of segregation. 



I. The mating DD x RR, and DR x Z>^?. II. The mating DR x 

 III. The mating DR x DD. 



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 



