144 



Journal of Agricultural Research 



Vol. VI, No. 4 



RESULTS OF THE DIFFERENT CROSSES 



If the factor for the black-and-white color is represented by B, the 

 hereditary constitutions are as follows: BB is always black-and-white; 

 bb is always red-and-white; Bb is always black-and-white in the male and 

 red-and-white in the female. All of the nine possible matings were 

 discovered, as shown in Table I. 



Table I. — Results of nine possible matings of Ayrshire cattle 



The expectations here presented are based on the most probable result 

 of each of the matings, considered on an individual basis with reference 

 to the number of animals produced by each type of mating, but without 

 figuring the proportions of the sexes as equal. From these data it would 

 appear that the black-and-white color of Ayrshire cattle behaves in an 

 ordinary sex-limited manner similar to the horns in sheep as discussed by 

 Wood (7) and the rudimentary mammae in swine as reported by the 

 writer (6). 



DISCUSSION 



Arkell and Davenport (i) have reported on the inheritance of horns in 

 sheep and have attempted to bring it under the ordinary sex-linked 

 scheme of inheritance by an ingenious system of inhibitors and horn 

 factors. Such an explanation was doubtless justified when horns in 

 sheep were the only character known in which the reversal of dominance 

 in the two sexes existed, but now that at least two other characters are 

 known in which an exactly similar system of inheritance occurs, it seems 

 unnecessary to assume the complexities hypothesized by these investi- 

 gators. Instead, the much simpler and probably more perfectly descrip- 

 tive explanation adopted by Wood (7) in his original paper seems more 

 logical. 



