402 ANIMAL BREEDING 



the father never acquired the abihty to lay eggs at any 

 season although he can transmit to his daughters a 

 marked ability to do so. 



Inheritance in Dairy Cattle. — The ability to pro- 

 duce large quantities of milk and butter fat depends on 

 the proper correlation of many structures and functions 

 and is therefore not governed by a single pair of genes. 

 It is nevertheless heritable, as is clearly shown by the 

 superiority of certain breeds, e.g., Jerseys. In breeding 

 for high milk production the breeder must keep all these 

 things in mind. Merely to enumerate some of them will 

 suffice to show the complexity of the problem. To turn 

 food into milk as economically as possible certainly re- 

 quires a good set of teeth, and a good digestive system, 

 and a type of metabolism which turns foods into milk in- 

 stead of into muscle or fat. That many of the genes 

 which control these things can be assembled in one race 

 is shown by the fact that the breeder has actually pro- 

 duced champion cows (e.g., Holsteins) which produce 

 30,000 pounds of milk per annum in place of the 3000- 

 4000 pounds produced by the scrub cow. Here again it 

 should be emphasized that high milk production is in- 

 herited from the male parent as well as from the female. 

 It should be noted, however, that the advantages of a 

 pure bred sire are not so great as in the example of the 

 fowl just given, because there the gene for winter egg- 

 production is sex-linked. 



Inheritance of Speed in Horses. — Since speed is 

 equally characteristic of both sexes, and since fast horses 

 are usually descended from parents both of whom were 

 fast, the inheritance of trotting ability has often been 

 cited by the advocates of the inheritance of acquired 

 characters as a case in point. If all cases were of this 

 sort it would be extremely difficult to give an acceptable 

 answer to this assertion, for it is an undoubted fact that 

 fast horses often beget fast offspring. The crux of the 

 question is whether it is the effect of training which 



