No. 596] 



EGG PRODUCTION AND SELECTION 



4 S3 



records also mature at an earlier average age than those 

 making poor records. Whether or not the mode of in- 

 heritance of fecundity in Ehode Island Reds follows 

 Pearl's theory is still uncertain. Since there is great 

 variability in the age at which the first egg is produced 

 and since its frequency polygon indicates, at least up to 

 305 days, the essential homogeneity of the Hock, we are 

 inclined to believe that the Reds are unfavorable material 

 for a solution of this question. More work, however, re- 

 mains to be done before this point can be cleared up. 



On Pearl's theory the continued selection of genetic 

 high producers and the continued use of their sons ns 

 breeders should in the long run tend toward an improved 

 egg production, even though individual pedigrees are not 

 kept, as he himself has pointed out. 



The rate at which the selection becomes effective de- 

 pends much on what classes are assumed to he available 

 at the start. In the following discussion it is assumed 

 that the matings are made on a scale sufficiently large to 

 permit the various matings to take place in the propor- 

 tions indicated. The scale required, however, is so large 

 that it would be scarcely practicable to test the matter 

 experimentally. 



In the first place, it should be pointed out that of the 

 nine genetic classes of males possible on Pearl's theory, 

 classes 5, 6 and 9 are not produced by any mating of class 

 1 and 2 females— the only classes laying 30 or more eggs 

 — with any class of males. Moreover, it can be shown 

 that if these three classes be assumed to be the only males 

 available and that if only class 1 females (1, L x , L 2 1 2 ) be 

 bred throughout the test and if the male offspring be bred 

 in each generation in the same proportion in which the> 

 were thrown by the preceding generation, at about the 

 seventh generation there would be male classes 1, 3 and 

 7 only, existing in the proportion of 1:2:1. Classes 2, 4 

 and 8 would indeed be present, but the three classes to- 

 gether would amount to only a little over 1 per cent, of 

 the population. This small percentage decreases one half 



