476 GENETICS IN RELATION TO AGRICULTURE 



shown by the evidence of C. B. Davenport. Black sheep mated together 

 produce only black sheep, and it is probable that the black sheep met 

 with occasionally in white flocks represent the cropping out of 

 homozygous recessives, like the occasional red calves in some herds of 

 black cattle. Wilson reports that black face and white face in sheep 

 represent a simple character contrast, the F\ heterozygote being gray. 

 There are, however, breeds of sheep which have gray faces, so that it is a 

 matter of question whether Wilson is not here again advocating too 

 simple an explanation. The inheritance of horns in sheep has been 

 subjected to Mendelian analysis, but questions of sex are involved in 

 this case, for which reason treatment is reserved for a succeeding chapter. 



Mendelism in Swine. About all that is known of Mendelian in- 

 heritance in swine deals with coat color. White is dominant to colored, 

 but segregation is rarely definite in F 2 , apparently* because white often 

 carries latent pattern factors which are responsible for the production of 

 belted and variously spotted individuals in segregating populations. The 

 belted pattern of Hampshire swine is dominant to uniformly colored coat, 

 and it is clearly independent of the particular color in the coat. The 

 evidence regarding spotting of the coat is conflicting, but at least one 

 type appears to be dominant. Black coat color is dominant to red, in 

 which respect it is like the corresponding color in horses and cattle. Red 

 in hogs may be of different shades, and like chestnut in horses, there is 

 evidence that the lighter shades are most easily maintained. There are 

 reports in the literature of roan swine, but the genetic constitution of 

 these is imperfectly known. As to other characters, the union of the 

 two toes found in mule-footed hogs is dominant to the normal condition, 

 and according to Spillman represents a single dominant factor difference 

 from the normal condition. 



Mendelism in Poultry. The Mendelian inheritance of comb char- 

 acter in fowls has been discussed in another chapter. The heterozy- 

 gous constitution of the Blue Andalusian fowl has, also, been discussed in 

 detail. Blue Andalusians mated inter se always produce Blue, White 

 Splashed, and Black Andalusian fowls in the ratio of 2 : 1 : 1 ; but black 

 birds mated with white-splashed ones produce nothing but Blue Anda- 

 lusians. The breeder, therefore, must maintain pens of black and 

 splashed white birds if he desires to produce progenies made up wholly 

 of Blue Andalusians. The fact that the Blue Andalusian never breeds 

 true, however, should be sufficient justification for refusing to recognize 

 it as a distinct breed. It is of interest to note that the Blue Breda bears 

 the same relation to a black- and a white-splashed form as the Blue Anda- 

 lusian. It is just, however, to note in passing, as Pearl in fact has pointed 

 out, that there is some doubt of the authenticity of these cases. They 

 require further investigation. 



