tor, then (designated in the table by the letter 

 I, its absence by i), will always be double in 

 the female and single in the male and, in the 

 gametes, will always be associated with the sex- 

 chromosome, which is designated through- 

 out by the symbol X; its absence by x. In 

 the zygote the single inhibitor is incapable of 

 preventing the development of the determiner 

 for the horn (JET) even when the latter is only 



simplex. But the double inhibitor is capable 

 of preventing the single horn (HJi) deter- 

 miner, but not the double determiner (HH~). 

 The table gives a summary of matings 

 used, their hypothetical somatic and gametic 

 composition, and the proportion of each sort 

 of zygote that will be formed in each sex. 

 The actual frequency of offspring derived 

 from each mating is given on the left of the 



