DOMESTIC ANIMALS 



si 



an ancestor which according to Galton's 

 law contributed only 1-256 of its char- 

 acters. In another instance a calf re- 

 verted in its color to a great-great-great- 

 great-grandfather. Atavistic charac- 

 ters appear most frequently when two 

 distinct breeds are crossed. Thus if two 

 races of pigeons are crossed, the blue 

 color of the original wild pigeon appears 

 in the progeny. In an experiment in 

 which Japanese waltzing mice were 

 crossed with white mice the offspring 

 could hardly be distinguished from the 

 common gray house mouse. Moreover, 

 the occasional appearance of stripes on 

 colts is supposed to be a reversion to 

 some striped wild ancestor. 



Prepotency i s another phenomenon 

 which deserves consideration as a factor 

 in variation. The progeny of unlike 



ature of animal breeding. The assump- 

 tion that one parent ever contributes 

 more than one-half to the sum total of 

 characters in the offspring has never 

 been proved. If such an assumption is 

 implied in the use of prepotency, it is 

 doubtful whether any such phenomenon 

 occurs in nature. 



As ordinarily used in popular jour- 

 nals and agricultural literature prepo- 

 tency means nothing more than the abil- 

 ity of a pure-bred animal (usually the 

 male) to transmit several of his char- 

 acters to his offspring from mongrel or 

 grade females. Now pure breeds are 

 established by a long series of matings 

 in which both parents are selected on ac- 

 count of their possession of certain 

 definite characters. These characters be- 

 come fixed, and no disturbing tendencies 



Fig. 20 — MODERN TYPES OF YOUNG ESSEX SWINE 



parents may be intermediate in appear- 

 ance between the parents, may resemble 

 one parent in one point and the other in 

 another feature, or may show none of 

 the characteristic features of one parent 

 while closely resembling the other. As 

 shown by Vernon and others these may 

 be cases of prepotency or may be merely 

 cases in which the characters of the par- 

 ents do not blend in the progeny. 



The term prepotency as applied to the 

 apparently unequal inheritance of char- 

 acters presupposes the existence of a 

 greater power in one parent than in the 

 other to impress its features upon the 

 offspring. Such a parent is said to be 

 prepotent or to have superior power in 

 transmitting qualities. The term pre- 

 potency is used very loosely in the liter- 



are allowed to creep in by admixture of 

 other blood. In other words all hered- 

 itary forces are directed along definite 

 lines. In a mongrel or scrub animal, on 

 the other hand, all sorts of miscellaneous 

 and more or less antagonistic tendencies 

 are mixed. There is no dominant set of 

 characters and no definite direction of 

 the heredity forces. 



Pure bred sires — Now when a pure 

 bred male is crossed on a mongrel 

 female his fixed and definite tenden- 

 cies give a certain amount of definite- 

 ness to the characters of the offspring. 

 The young are said to resemble the 

 father more than the mother. But 

 there is nothing strange about this phe- 

 nomenon, in fact it would be highly 

 remarkable if it should fail to occur. 

 Prepotency is a useful term, however, 



