Oct. 7, 1918 Crosses between Dairy and Beef Breeds of Cattle 



47 



it would seem that Kayan has been shown homozygous for the polled 

 character, for if Kayan is considered heterozygous for the polled char- 

 acter, we have the impossible ratio of 17 polled to i horned, where the 

 expectation is equality. Another assumption is left open: The scurred 

 animals are really homozygous for the horned factor. This hypothesis 

 seems unlikely on the following grounds: Scurs are present only where 

 polled individuals are also in the stock. The inclusion of the scurred 

 animals with the polled ones always improves back-cross ratios of 

 polled X horned crosses, whereas the inclusion of scurred individuals 

 with the horned group makes the ratios far from probable. 



The same kind of case occurs in No. 31 out of the Aberdeen- Angus 

 cow Eventime 4th. Since it has not been possible to test her genetic 

 composition in so thorough a manner as that of Kayan, the case may 

 be due to Eventime 4th being heterozygous for the horned factor. 



Thus, we have two exceptional cases for polledness which demand a 

 supplementary hypothesis to explain their appearance. 



Spillman {41) says that scurs may develop to considerable size, but 

 are loose and hollow. It is interesting in this connection, however, to 

 point out that 8 loose- to 3 tight-scurred animals occur, a ratio corre- 

 sponding well with the expectation of the E2 population for a separate 

 factor for loose and tight scurs. From this the most probable explana- 

 tion would seem to be that loose and tight scurs are due to a simple 

 Mendelian factor and not due to any inherent quality of being scurs. 



In another paragraph in the same paper Spillman says that males are 

 more likely than females to have scurs. This statement, however, is 

 not supported by evidence, and in fact is contradicted by Lloyd-Jones 

 and Eward (20), who say their data — 



give no evidence that sex is in any way connected with the inheritance of these 

 characters [Homed and polledness]. 



These investigators offer numerical data on the frequency of scurs. 

 In 78 cases 6 were scurred and 2 horned. It will be seen that this 

 frequency is much below that of the data of the author. Unfortunately 

 Lloyd- Jones and Eward do not sex their data; but it is possible to 

 group the data of the present author in relation to sex, as is seen in 

 Table XXVII. 



Table XXVII. — Relation of sex to polledness" 



a This table is based on descriptions made before any idea of the infliioiice of testicular secretion on the 

 production of horns in the licterozyRous individual was thought ol. 



6 This male is recorded with loose scurs just under skin. He died and was put away before this could be 

 checked. 



