F. Pitt 287 



Variability of the Somatic Expression of the Factor for White : 

 Promise 2nd, the first pure recessive to appear in the above mentioned 

 family, was not of the extremely badly marked type such as her daughter. 

 Pay, shown on PL VII, fig. 3, but was a grade — 1| animal; however, 

 her progeny have proved her pure for the white factor, and her first calf, 

 as already mentioned, was an exceedingly white heifer. Her produce, by 

 heterozygous bulls, have been 3 TTTT, and 4 iVTF, the three recessives 

 being particularly badly marked. I have mentioned this to show that, 

 though the somatic effect of the white factor varies somewhat, any beast 

 having white beyond the shoulders may be confidently assumed to be a 

 homozygote of the constitution WW. Of the four cows proved to be pure 

 for white with which Bounds Chance (NW) was mated, two, Princess 2nd 

 and Promise 2nd, were rather too white and two. Olivette and Pay, were 

 exceedingly badly marked, yet genetically they behaved in a similar way. 

 The latter had between them eight calves, four being normal, to four with 

 too much white. The other cows had also eight calves, three with typical 

 markings, and five badly marked. This shows, as stated before, that not 

 only is the factor for excessive white variable in its somatic expression, 

 but that individuals in which it does not reach its full expression are 

 identical genetically with those in which it is fully displayed. 



Summary : The above evidence shows that extra white in Hereford 

 cattle acts as a simple Mendelian recessive to the normal type of 

 markings, normal and badly marked cattle occuring in the ratio of 3 : 1 

 when heterozygous individuals are mated together. The factor for 

 excessive white has been styled herein the W factor, the capital letter 

 being used because the disappearance of pigment from the white areas 

 is probably due to the presence of a special factor, and not merely to 

 the absence of that for the typical markings. This conclusion is arrived 

 at because the white face of the Hereford is dominant in crosses with 

 most other breeds of cattle, and it is logically impossible to com- 

 prehend how a thing which does not exist can dominate that which is 

 present. The dominance of the white face must be due to some special 

 factor or gene, for the absence of factors for colour could hardly cause 

 the disappearance of those for pigmentation from the gametes of fully 

 pigmented breeds with which the Hereford happens to be crossed. If 

 the white face and extremities are due to the presence of a' special factor 

 it becomes apparent that the extension of the white is almost certainly 

 due to another similar factor, that which has been styled W. This can 

 only show itself in the absence of the factor for the normal amount of 

 pigmentation. The expression of the factor W varies somewhat, and 



