Jan. is. 1921 Inheritance of Syndactylism and Color in Swine 601 



hand, and Duroc-Jersey or Tamworth on the other. Selecting on the 

 basis of minor factors for the extension of black and for the dilution of 

 red to white gave the Berkshire color type, while selecting minor factors 

 for the restriction of black and for the intensity of red gave the Duroc- 

 Jersey type. In our crosses the self -black of the mule-foot does not act 

 like the black of the Berkshire with its peculiar pattern, but whether this 

 is due to a real difference in their genetic factors for black or is due to 

 variable spotting factors in the Berkshire as compared with the self of 

 the mule-foot remains to be shown. The six white points of the Berk- 

 shire may represent a highly selected spotting factor, or factors, with 

 numerous modifiers. By crossing such Berkshires to Duroc- Jerseys one 

 would expect to obtain a complex spotted hybrid. The mule-foot and 

 the Duroc-Jersey are both self-colored and, as our experiments indicate, 

 a cross between the two involves no striking spotting factors but shows 

 clear-cut segregation between self-red and self-black. We may, there- 

 fore, regard black (B) as a dominant allelomorph to red (b) in our crosses. 



The original mule-foot boar (BB) was mated to Duroc -Jerseys (bb) 

 and gave about 250 F x hybrids (Bb) which were self-black. The 6 F x 

 sows mated to a Duroc-Jersey boar gave 19 blacks to 23 reds in the F 2 

 generation, where 21 of each kind is the calculated ratio. The recessive 

 F 2 red segregates gave 18 F 3 reds. The F 3 reds when mated inter se gave 

 12 F 4 reds. Extracted recessive reds, therefore, breed true. The total 

 results indicate that black and red are allelomorphs in this cross in swine, 

 black being dominant to red. In all of the foregoing discussion the term 

 red includes red, yellow, lemon, and cream shades — that is, any form 

 showing red pigment but no black. 



In any wide cross between two distinct varieties like the Duroc-Jersey 

 and mule-foot there are many factorial differences involved, and we are 

 not surprised to find numerous new variations in the F 2 generation and 

 subsequent hybrids which were not seen in the parents. Thus, we 

 observed an occasional white spot on the feet or hoofs, white spot on the 

 upper lip, animals with varying amounts of roan, more variation in size, 

 and the like. Among the more striking variations seen in the F 2 gen- 

 eration were the grades of intensity and dilution of red pigment. Although 

 red in the Duroc-Jersey varies somewhat, the red F 2 segregates varied 

 much more than the original Duroc-Jersey parents. The black of the 

 F t and F 2 hybrids, on the contrary, did not vary perceptibly. This 

 seems to indicate that diluters of red may be carried by black swine but 

 that such diluters do not affect black. In this cross the original black 

 mule-foot sire evidently contributed diluters of red to the black F x 

 hybrids; and such diluters segregated, giving more variability in red in 

 the F 3 generation. We can hardly suppose that the Duroc- Jerseys con- 

 tributed the factors for this dilution, because Duroc-Jerseys mated inter se 

 do not show such dilute forms as we observed among our red segregates. 

 Samples of hair from each individual were saved. Comparing all F, reds 

 with each other, we classified these around four more or less arbitrary 



