26 A MANUAL OF MENDELISM 



(12) The number of pure-breeding individuals in any 

 one group is equal to the number of individuals in the 

 smallest group in the set. 



(13) If two or more groups in the hybrids' progeny 

 are inseparable, then the number of groups will be one 

 less than the normal for every group which is inseparable 

 from another, and the number of individuals in one of 

 the groups will be the sum of the numbers in the in- 

 separable groups together. For instance, if the first 

 two groups in a two-pair set of four be inseparable, 

 there will then be three apparent groups in the ratio 

 12 : 3 : 1, thus : 



X X X X 

 Y_^ Y y 



12 : 3 : 1 

 If the last two groups be inseparable, there will be 

 three apparent groups in the ratio 9:3:4, thus : 

 X X X X 



Y y Y y 



9:3: 4 



If the first three groups be inseparable, there will be 

 only two apparent groups in the ratio 15 : 1, thus : 

 X X X X 



Y y Y y 



15 : 1 



If the last three groups be inseparable, then there 

 will again be only two apparent groups, but in the ratio 

 9 : 7, thus : 



X X X X 

 .Y y Y y 



9 : 7 



