110 



Research in Animal Breeding 



[May, 



RESEARCH IN ANIMAL BREEDING. 



II. 



R. C. PUNNETT, F.K.S., 



Professor of Genetics, University of Cambridge. 



In the first article of this series, published in the April 

 issue of the Journal, Prof. Punnett dealt tcith coat colours 

 in cattle as an illustration of simple Mendelian inheritaiice. 



In the case selected for illustrating simple Mendelian inheri- 

 tance, viz., black and red coat colours in cattle, one of the 

 members of the alternative pairs of characters is completely 

 dominant to the other. The black animal that carries red germ 

 cells is quite as black in appearance as the true breeding black 

 that carries black germ cells only. This feature of complete 

 dominance is found frequently in animals, but there are other 

 cases in which it is possible to distinguish by appearance, the 

 form that carries both kinds of germ cells. Roan Shorthorns 

 provide an illustration. 



No breeder has succeeded in establishing a strain breeding 

 true to roan, for such animals, when bred together, always 

 throw reds and whites in addition to roans. Statistical examina- 

 tion of the herd books by several writers suggests that two kinds 

 of germ cells are concerned, viz., " red " and " white." When 

 two " red " germ cells meet, a red* animal results, and such 

 animals breed true to red; also, when two " w T hite " germ cells 

 meet, the result is a white, and such animals breed true to white. 

 When, however, a red is crossed with a white, as shown in Fig. 3, 

 a union is effected between a " red " and a " white " germ cell. 

 The resultant animal is a roan, more or less intermediate in 

 appearance between full red arid white. This animal, formed by 

 two unlike germ cells, carries both " red " and 4 ' white " germ 

 cells in equal numbers; consequently, when roans are mated 

 together equal numbers of " red " and " white " ova are 

 fertilized by equal numbers of " red " and " white " sperms. 

 Each red ovum has an equal chance of being fertilized by a 

 " red " or by a " white " sperm; in the former case it will give 

 a pure red animal, and in the latter a roan. Also, each " white " 

 ovum has an equal chance of being fertilized by a " red " or 

 " white " sperm; in the former case a roan animal will result, 

 and in the latter a white. Roans mated together, as shown in 



* Both reds and roans may have white markings, especially on the belly, 

 but these appear to be independent of the roan character. 



