BREEDING POULTRY FOR EGG PRODUCTION. 167 



D352 belonged to a low fecundity genotype, in spite of her 

 individual high laying record. 



THE EPFliCT OF THE; SEiLEXTlON OF FE^CUNDITY GE^NOTYPES. 



Let us now consider the bearing of the results so far set forth 

 on the problem of selection. Taking first the question of the 

 effect of selection for fecundity within a population it is plain 

 that if different degrees of fecundity have a genotype basis, as 

 the facts above presented and a considerable mass of data of a 

 similar kind, which owing to lack of space can not be given 

 here would appear to indicate, then the results following selec- 

 tion will depend entirely upon the genotypic constitution of the 

 population. If high fecundity genotypes are present they can 

 be isolated by selection. If they are not present selection of 

 high laying hens will not change the average production of the 

 flock. 



The aim of the selection experiments since 1907 has been to 

 discover and propagate separately genotypes of high fecundity 

 and genotypes of low fecundity, all the birds being taken from 

 the same general flock. The results of this work are shown in 

 the following table and in Fig. 84. This table is to be regarded 

 as a continiiation of that given on p. 156, supra, which shows the 

 results of m.ass selection for high fecundity in the same stock. 



Effect of Selection for Fecundity within the Population 



1907-08. Mean winter production of general poptilation iS-92 



1908-09. Mean winter production of all high fecundity lines 54-i6 



1908-09. Mean winter production of all low fecundity lines 22.06 



1909-10. Mean winter production of all high fecundity lines 47-57 



1909-10. Mean winter production of all low fecundity lines 25.05 



1910-11. Mean winter production of all high fecundity lines SO.58 



1910-11. Mean winter production of all low fecundity lines 17.00 



The results indicate the effectiveness of this method of selec- 

 tion. It should be understood, of course, that only those pedi- 

 gree lines are included in the high line averages which uni- 

 formly in each generation show high fecundity. A similar con> 

 sideration applies to the low line averages. 



Let us now consider briefly the question of the effectivenesb 

 of selection zvithin the genotype. According to the "pure line" 

 concept we should not expect selection of high or low indi- 

 viduals belonging to the same genotype to produce any effect, 



