64 Mendelian Experiment with Cattle 



breeds of sheep, the heterozygous males are horned, while the hetero- 

 zygous females are hornless. The horn development in the hybrid male 

 has been shown to be dependent on a hormone secreted by the testis, 

 and horn growth is stopped (again in the hybrid) by castration. The 

 analogous experiment has not been performed with cattle. It is to be 

 noted that the F, males were all castrated. 



(h) Colour. 



The ^1 generation, with the sole exception of the red calf F^ 3, were 

 either dun or black. With regard firstly to the behaviour of black and 

 red, we should conclude that black is dominant, red recessive. Matings 

 of the heterozygous ^i blacks inter se {F^ females 6, 7, 8 and 9) produced 

 16 ^2 of which 13 were black, 3 red, against an expectation of 12 and 4. 

 These results may be regarded as in complete accord with the accepted 

 view, originally advanced by Spillman(ll) that red behaves as a simple 

 recessive to black. The red calf F^ 3 calls for further explanation, but a 

 highly probable explanation is at hand, namely that its Aberdeen-Angus 

 sire J. J. 3 was heterozygous for black. The appearance of the recessive 

 reds in pure bred Angus herds, already referred to, renders such an 

 explanation inherently probable. Moreover the bull in question was in 

 use by a local farmer for crossing with heifers of mixed colours, and with 

 them he begot a large proportion of red and red-roan calves. In this 

 connection it may be said that the sires A A 2 and A A 4c left no red 

 calves in the herds where they were used on cattle of various colours. 

 AAl cannot be regarded as having been tested. 



The dun x black matings constitute a more complex problem. The 

 hypothesis thus far proposed must first be considered. Wilson (12 and 

 13) has proposed a series of Multiple allelomorphs or " polygamous 

 factors," any one of which behaves as a Mendelian alternative to any 

 other. In so far as the present experiment is concerned, three factors 

 would be concerned, viz. B (black), R (red), and L (Light Dun). The 

 following are the colours allotted by Wilson to the various possible factor 

 combinations : 



BB Black (homozygous) 



BR Black (heterozygous) 



BL Dun 



RR Red 



RL Yellow 



LL Light Dun 



