BLENDING CHARACTERS 185 



mammals, when closely inbred for many generations, tend 

 to become sterile and lose in vigour. Breeders, therefore, 

 have to bring in new blood, that is, they are obliged 

 occasionally to cross with a race which is not very nearly 

 related to the particular strain they are developing. Thus 

 in mammals, we should expect many cases where no segre- 

 gation of characters occurred, and this is exactly what we 

 find. For instance half-bred sheep derived from Border 

 Leicester rams and Cheviot ewes, when inbred, continue 

 to exhibit blended characters and show no signs of segre- 

 gation. The same thing has happened in many cases in 

 crosses in cattle. 1 The case of a particular calf is worth 

 quoting. The sire was a cross between a pure Hereford 

 and a shorthorn-cross bull. The dam was a pure black 

 polled Aberdeen Angus cow. The calf was a creamy 

 white heifer with a black muzzle and black hair on 

 insides and tips of ears. As well as in its colour, the calf 

 showed other points of resemblance to the Chillingham 

 white cattle, a very ancient breed. 2 Even in domesticated 

 plants many characters are found which do not appear 

 to follow the Mendelian law. 3 Mendel himself with 

 Hieracium* did not obtain Mendelian results, and the 

 same has happened in other cases. It is thus evident 

 that all characters even in domesticated races do not follow 

 the Mendelian law. 



When we come to consider natural races, we find that 

 such characters as frequently follow the Mendelian law in 

 domesticated races, rarely do anything but blend when 

 crossed. There are some that apparently do segregate, but 

 this is the exception rather than the rule. In fact, but 

 a very few instances of the segregation of parental char- 



1 Thomson, J. A., Heredity, pp. 336, 377, 378, 384, 1908. 



2 Thomson, loc. cit., p. 378. 



3 Report of Lecture by Professor Weldon, Lancet, March 25, 1905. Reference 

 to Tschermak's experiments. 



4 Mendel, G. J., " tiber einige aus kiinstlicher Befruchtung gewonnene 

 Hieracium-Bastarde," Verhandlung des Naturforschaftlichen Verein in Briinn, 

 1869. 



