38 



The Journal of Heredity 



3. Thf third hypothetical factor is 

 suggested to account for the frecjuent 

 occurrence of an isohited spot of color 

 around the eye, a region commonly 

 pigmented in white spotted mammals 

 in general. 



4. Pigmented or "dirty" nose is 

 supposed to be due to a fourth factor. 

 It is regarded as a blemish, arising 

 from the imdesired presence of black 

 or brcnvn pigment in the skin of the 

 nose, which should be unpigmented. 



5. The fifth hypothetical factor re- 

 lates to the general color of the coat, 

 which should by present breed stand- 

 ards be dark red, of a "deep plum tint 

 called claret or purple." But many 

 indi\iduals of the breed are of a lighter 

 shade known as "yellow," which ap- 

 pears to be dominant oxer the desired 

 dark shade. 



This five-factor scheme of modifying 

 factors forms an excellent working 

 hypothesis for studying the problem 

 outlined, but it has not been utilized 

 as fully as the available records ap- 

 parently warrant. For the records, we 

 are told, consist of photographs of each 

 calf born in the herd, which may be 

 compared with the patterns of dam, 

 sire, and other relatives, a very ex- 

 cellent system. A system of grading 

 each animal accurately as regards ex- 

 tent of pigmentation was also worked 

 out, which is copied in Fig. 28. But in 

 describing the obser\ed results no use 

 is made of this grading scheme. We 

 are told the results of particular 

 matings, nt^t in terms of the grades of 

 sire, dam, and offspring, but only in 

 terms of the assumed factors. If an 

 analysis has actually been made of the 

 pedigrees published, in terms of grades 

 as well as in terms of assumed factors, 

 that analysis should be given to the 

 reader, that he may judge for himself 

 whether the hypothetical scheme fits 

 the facts well or ill. 



Of the five assumed Hereford factors, 

 three are suppf)sed to be dominant and 

 two recessive. The whitening factor is 

 regarded as recessi\e, the darkening 

 factor as dominant. Why, it might be 

 asked, ma\' the analysis not be simpli- 

 fied by treating "dark" and "white" as 

 dominant aiul recessive members re- 

 sj)e(ti\el\' of a single set of allelo- 

 morphs? Does either one breed true? 



That is realK- the crucial |)oiin which 

 the published records do not cover. In 

 work with other spotted mammals, no 

 grade of white spotting has been found 

 to breed true. And so it seems very 

 doubtful that any particular grade of 

 Hereford cattle will be found to breed 

 true. Indeed the author assumes that 

 "the factor for excessi\e white is vari- 

 able in its somatic expression" and in 

 particular that it acts as a partial in- 

 hibitor or neutralizer of dark. Accord- 

 ingly it seems very doubtful whether 

 two modifying factors acting in oppo- 

 site directions are sufficient to account 

 for such graded \ariation as other 

 white spotted mammals manifest, and 

 such as the grading scale of Fig. 28 

 indicates to occur among Hereford 

 cattle, unless we assume that the 

 factors themselves fluctuate, an hy- 

 pothesis commonly regarded as un- 

 tenable, for good and sufficient reasons. 



The scheme outlined is too simple 

 also as regards the inheritance of "pig- 

 mented nose." If pigmented nose is, a 

 assumed, due to a simple dominant 

 factor, it should be the easiest thing in 

 the world to get rid of it, by simply 

 breeding from clean nosed animals 

 (recessives). But such is apparently 

 not the case. The author says "Dirty 

 noses are greatly disliked by breeders, 

 who in\arial)ly eliminate the bearers 

 of them from their herds, yet dark 

 noses continue to crop up in even the 

 best bred strains of cattle." The ex- 

 perience of Ciuernsey cattle breeders 

 supports this view. 



As regards the assumed one-factor 

 difference between "yellow" and 

 "claret," if the shades of color obtained 

 are carefully clat^sified, it seems dr)ubt- 

 ful whether segregation will be fovnul 

 to occur on a I :l basis. Dunn has not 

 found such to be the ca.sc in crosses of 

 yellow with red mice, where similar 

 conditions obtain. 



The paper under review is to be 

 highly commended as a pioneer work 

 in a difficult but inviting field, one of 

 practical no less than of theoretical 

 interest, but in the light of the experi- 

 mental work on rabbits, rats, and mice, 

 the conclusions outlined are to be ac- 

 ci'pted with reserve, as probably pre- 

 .senting a scheme of m(Klif>ing factors 

 much simpler than the actual one. 



