EFFECTS OF INBREEDING ON THE SEX RATIO 9 



litters containing an excess of females. Reference data showing 

 the proportion of males and females produced in the various 

 generations of this series are given, by litter groups, in table 3. 

 The data comprise a total of 1656 litters containing 12,336 

 individuals. 



The summary for each of the four litter groups of the B series 

 (table 3) shows that the sex ratio was at its lowest point in the 

 first litter group, and then tended to rise in each of the subsequent 

 groups. This is a reversed relation of the sex ratios to that shown 

 in the litters of the stock controls (table 1) and in the litter groups 

 of the A series (table 2), and w^ould seem to indicate that some 

 agency, other than environment or the age of the mother, had 

 influenced the relative proportion of the sexes in this series of 

 animals. 



In order to compare the sex ratios in the litters sired by inbred 

 males with the sex ratios in the litters sired by stock males, the 

 sex records for the first and second litters produced in each 

 generation of the two series were ' combined, as were also the 

 records for the third and fourth litters. Table 4 shows the 

 combined data for the litter groups of the A series ; table 5 shows 

 similar data for the litter groups of the B series. 



Reference to the data given in table 4 and in table 5 will be 

 made later. 



To facilitate an analysis of the results obtained in the A 

 series of inbreds, the data, as shown in table 4, were combined in 

 generation groups (table 6). This grouping of the data was 

 purely arbitrary. It seemed useless to compare such large series 

 of records generation by generation, or even to combine the records 

 for two succeeding generations. Since after the sixth generation 

 the selection of breeding animals was made according to a 

 definite plan, it would seem that, logically, the data for the first 

 seven generations should form one group. Such a group, how- 

 ever, was too large for the purpose of ascertaining whether 

 selection produced a varying effect in different generations. It 

 was finally decided to make a total of eight groups, each of which, 

 except the first, should contain the data for three generations. 

 Because of the small number of individuals, records for the first 

 four generations were combined in one group. 



