Jan. is, 1921 Inheritance of Syndactylism and Color in Swine 599 



No statement is made regarding segregation. Kronacher (4) implied 

 that the character was transmitted pure after hybridization, for he says : 



Der Zuchter v. Dtuiin-Kozicky liess im Jahre 1888 ein derartiges, gelegentlich 

 erhaltenes Einhuferschwein (polnisches Landschwein) von einem Yorkshireeber 

 decken und erhielt zur Halfte (5 von 9) solche Einhufernachzucht, die ihr charakter- 

 istisches Merkmal rein Eitervererbte. 



It is difficult to know whether Kronacher really means that these 

 mule-foot hybrids gave no cloven-footed segregates or that the character 

 when transmitted showed no contamination after the cross and was 

 therefore "pure." Reference to the original source quoted by Kron- 

 acher leaves no doubt as to segregation, for von Dabrowa-Szremowicz 

 (1) states explicitly that, in attempting to fix the mule-foot character, 

 sporadic cases of cloven-foot crop out. He says : 



Da bei den Schweinen es uberhaupt schwer ist, eine einheitliche und gleichmassige 

 Abart festzustellen, so treffen sich aueh noch bei den meinigen vereinzelte Falle mit 

 gespaltenen Hufen. 



It is clear, then, that this case agrees with both Spillman's and our 

 own observations on dominance and with our observations on segrega- 

 tion. 



The original mule-foot boar in these crosses was undoubtedly homozy- 

 gous (MM) in the factor for syndactylism, for every one of his offspring, 

 about 250, showed the mule-foot character. Six F x sows (Mm) were 

 bred back to the cloven-foot Duroc- Jersey (mm), and each one gave 

 both mule-foot and cloven-foot segregates. The total F 2 generation 

 thus produced was 17 mule-foot +25 cloven-foot, where theory calls 

 for 21 of each kind as the most probable result. The deviation, 4, is no 

 larger than one might reasonably expect as a fluctuation of sampling 



/deviation 4 \ 



I v— r\ = = 1-83 J. It we add to these results those re- 



\probable error 2.19 °J 



corded by von Dabrowa-Szremowicz, we obtain 22 mule-foot+ 29 

 cloven, where 25.5 is the most probable value. In this total, the cal- 

 culated and observed results show even a closer agreement, for 

 deviation _ 3.5 _ ^ 

 probable error 2.41 



In experiments with the larger domestic mammals the usual apology 

 for small numbers must be made, for they often obscure the real facts. 

 In making our results a test against a monohybrid Mendelian hypothesis 

 we must not overlook the fact that our data might also admit of a dihybrid 

 interpretation with interaction of two factors to produce the mule-foot 

 character. For example, if mule-foot were due to the interaction of 

 X and Y, then the original mule-footed grandparent was XXYY and, 

 mated to xxyy females, gave XxYy in the Fj generation. Back-crossing 

 to xxyy would thus be supposed to give: 



XxYy Xxyy + xxYy + xxyy 



25 per cent mule-foot 75 per cent cloven-foot 



