152 MUTATION. 



ation ressemble the wild species A ABB. In other words the 

 male will have horns and the females will be hornless. Matings 

 of such AaBb hybrids inter se will give the customary g AB, 

 3Ab, 3aB and lab individuals. For males this means: gAB, 

 horned, like the wild, 3aB horned, like the long-horned breed, 

 $Ab horn-less, like the rams of the horn-less breed and dab, 

 probably horned For females the result will be gAB, horn- 

 less as the wild breed, 3 A b horn-less as the horn-less breed, 

 3aB horned like the forned breed and lab probably horn-less. 

 In all for males, 12 horned to 4 horn-less, which is 3 : i and for 

 females 12 horn-less to 4 horned, which is also 3 : i. This tallies 

 very well with the facts as observed by Woods. It is preferable 

 in three points, firstly because it does not need the additional 

 hypothesis that heterozygotes are markedly different from 

 homozygotes, secondly because it accords better with the 

 existence of pure breeds with all stages of horn-development, 

 ancf thirdly, because it explains the production of horned 

 daughters by horn-less parents, e. g. the production of horned 

 aaBb females by an A abb father and AaBB mother, both 

 horn-less. 



We may not forget that, at the time when Woods published 

 his results, it was still rather universally believed that the genes 

 were things which each "determined" a single organ or a 

 single quality of an organism. It is obvious, that the work was 

 begun with the assumption, that he was dealing with a single 

 "unit-factor," determining horns. And it is probably for the 

 same reason, that Woods assumed that the horned breed 

 should have a gene more than the hornless, rather than re- 

 versely, notwithstanding the fact that he was perfectly free 

 to choose either hypothesis. 



A series of genotypically different families, which each has 

 a certain character developed to an extent of its own, but 

 in which in every strain the males difter materially from the 

 females such as we encountered in the sheep, must be of rather 

 common occurr< nee. Another good example is that of the 

 Silver Wyandotte. In this species the males are very much 



