Wright: Color Inheritance in Mammals 



37 



into each other and there was no evi- 

 dence for segregation of an outstanding 

 unit factor either for extension of black 

 or intensity of red. The indications are 

 that both Berkshires and Durocs possess 

 the same partial extension factor and 

 the same intensity factor. The genetic 

 evidence suggests that both have l^een 

 selected from a sandy colored hog with 

 black spots. From such a foundation 

 (as far as color is concerned), Durocs 

 (and Tamworths) have been selected 

 for restriction and intensity, so produc- 

 ing sohd red breeds, while Berkshires 

 (and Poland-Chinas) have been selected 

 for extension and dilution, so producing 

 black breeds with white points. Selec- 

 tion appears to have worked through 

 minor factors leaving the major factors 

 essentially the same in all four breeds.^'* 

 In Severson's crosses, extension of 

 black appears to be associated with 

 dilution of red. Whether this is merely 

 accidental or because the paler parts of 

 the coat are the last to be invaded by 

 black or because there is a real physio- 

 logical interrelation is not clear. Under 

 the last head it is conceivable that com- 

 petition between the processes of form- 

 ing black and red pigment might lead 

 to such a correlation. 



CONCLUSIONS 



The conclusions reached may l:)e sum- 

 marized in the scheme of factois given 

 below. A system of three allelomorphs 

 in the extension series is adopted for 

 simplicity. There may equally well be 

 two sets of independent factors as far as 

 present evidence goes. The formulae 

 which must be ass'gned to certain of the 

 breeds, are also given below. 



Yorkshires may be assigned minor 

 factors for extension, intermediate in ef- 

 fect between those of Duroc- Jerseys and 

 Berkshires. Black spotted segregates 

 appear in Yorkshire — Duroc crosses in 

 the second generation, while the black 

 spotted segregates from Yorkshire — ■ 

 Berkshire crosses have less black than 

 pure Berkshires. Yorkshires also proba- 

 bly have minor factors for dilution since 

 Yorkshire by Berkshire does not produce 

 red or black-red hogs in Fo. Whether 

 any of the hogs were sandy colored 

 rather than white in Fo in his crosses is 

 not mentioned by Smith. This would 

 of course be expected on the above hy- 

 pothesis. Further evidence for the pres- 

 ence of minor factors for dilution may 

 be found in Simpson's ^^ cross of York- 

 shire with Tarn worth. In F2 he found 

 not only the red of Tamworth and the 



DD, Dd 



EyEy White to roan 



EyEb White to roan 



EyEh White to roan 



EbEh White or roan -1- black spots 



EbEh Black 



EhEh Black 



dd 



Sandy to red 



Sandy to red 



Sandy to red 



Sandy or red-|-black spots 



Black 



Black 



Yorkshire (white) 

 Chester (white) 

 Tamworth (red) 

 Duroc Jersey (red) 

 Berksnire (black-white) 

 Poland China (black-white) j 

 Hampshire (black-white) 

 Essex (black) 

 Wild boar (agouti) 



EyEy dd vv 



EbEb dd vv-f minor factors for intensity of red and restriction 



of black. 

 EbEb dd vv+minor factors for dilution of red and e.xtension 



of black. 

 EhEh dd VV 

 EhEh dd vv 

 EhEh dd VV+ Agouti factor or factors. 



^* The following quotations from C. S. Plumb's "Types and Breeds of Farm Anim.als" are 

 of interest in this connection. "In 1789, Cully wrote: 'They (Berkshires) are in general reddish- 

 brown with black spots upon them'" (p. 472). Youatt is quoted as stating that, about 1830, 

 Berkshires were "sandy or whitish-brown spotted with dark brown or black' ' (p. 473). Plumb 

 states in regard to Poland-Chinas: "Thirty years ago, large white or sandy markings were com- 

 mon on the body" (p. 490). In regard to Duroc-Jerseys he states: "Eminent authorities think 

 that much of the Duroc -Jersey pig is descended from the sandy-colored Berkshire" (p. 506). 

 Tamworths seem to have been solid red as far back as known. 



15 Simpson, Q. I. 1914. Loc. cit. 



