152 MUTATION. 



ation ressemble the wild species AABB. 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 9 AB, 

 3 Ah, 3uB and lab individuals. For males this means: gAB, 

 homed, like the wild, jaB horned, like the long-homed breed, 

 3Ab horn-less, like the rams of the hom-less breed and dab, 

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

 less as the wild breed, 3Ab horn-less as the hom-less breed, 

 3aB homed like the fomed breed and lab probably hom-less. 

 In all for males, 12 homed to 4 hom-less, which is 5 : 7 and for 

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

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

 in three pomts, firstly because it does not need the addjtional 

 hypothesis that heterozygotes are markedly different from 

 homozygotes, secondly because it accords better with the 

 exist' nee of pure breeds with all stages of horn-development, 

 and thirdly, because it explains the production of homed 

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

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

 hornless. 



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

 his results, it was stUl rather universally beheved 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 h^ 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 differ 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 



