292 Colour and Markings in Pedigree Hereford Cattle 



Though the records of a number of matings show that the presence 

 of pigment round the eyes is dominant to its absence, the evidence is 

 insufficient to show to what extent, if any, the factors affect each other. 

 It is certain that the heterozygotes tend to exhibit less pigment than 

 the pure dominants, but the accurate division of one from the other 

 by appearance alone is a somewhat difficult matter, so it is probable 

 that some individuals classed as Rr are really RR (the " red-eyed " 

 character is hferein styled RR), and as I have already mentioned it is 

 possible that the presence of the factor for normal markings tends to 

 inhibit the full expression of that for " red-eyes " ; only breeding will 

 reveal the genetic constitution of these doubtful animals, but as, at the 

 time of writing, the majority are calves or yearlings it will be some 

 years before any certain conclusion can be arrived at. 



The results achieved so far may be summarised as follows : 18 cows, 

 believed Rr, had by 5 Rr- bulls, 54 calves, 42 red-eyed to 12 white-eyed 

 recessives. 42 : 12 is a fair approximation to the 3 : 1 ratio which in this 

 case gives an expectation of 40*5 : 13"5. 



As already explained too few of the red-eyed class have been tested 

 by breeding for their genetic constitution to be anything but guess 

 work. Some have hardly any pigment round the eyes, others a con- 

 siderable amount, the colouring being so heavy in the case of seven as 

 to make one convinced that they at any rate are homozygous for the 

 character, which gives a result of *I RR : 35-Rr : 12rr. This makes the 

 RR class too small, expectation being 13"5 : 27 : 13*5. 



Matings of heterozygotes with recessives give the following results: 

 7 cows of the constitution Rr had by 5 rr bulls 17 calves, 8 red-eyed to 

 9 white-eyed. Three rr cows when mated with an Rr bull had 10 

 calves, being 4 J2r to 6 rr. Total 12 Rr : \b rr , expectation being 

 13-5 : 13-5. 



Considering the smallness of the figures dealt with the results 

 support the general conclusions. 



With regard to Rr x RR matings the evidence is unfortunately 

 still more scanty, but what there is agrees with theoretical anticipations. 



A RR cow had four calves by an Rr bull, two of the produce being 

 undoubtedly pure dominants, and the other two heterozygous for the 

 character. This cow also had a calf by a white-eyed bull which was 

 clearly of the constitution Rr. 



Summary: It is evident from the foregoing evidence that the presence 

 of pigment round the eyes of Hereford cattle is dependent on a single 

 dominant factor, which is allelomorphic to its absence, and that this 



