EFFECTS OF INBREEDING ON THE SEX RATIO 25 



The sex ratios in the various groups of Utters obtained by the 

 mating of stock females with males from the tenth to the eigh- 

 teenth generations of the B series of inbreds showed a much nar- 

 rower range of variation than that found in the litters sired by 

 males of the A series of inbreds, although the number of litters 

 produced in the two series was about the same. The 117 litters 

 in this group gave a sex ratio of 96.2 cf : 100 9 , which was 9 

 points below the norm. Any significance that this ratio might 

 seem to have, when taken alone, is apparently annulled by the 

 fact that the sex ratios for the other litters groups were also below 

 the norm, whether the sires of the litters came from the A or from 

 the B series of inbreds. Moreover, the probable error of the mean, 

 calculated from the averages for the various sets of litters, was so 

 large in every case that the differences between the sex ratios of 

 the various groups were rendered valueless. 



The 242 litters in this series gave a sex ratio of 99.1 cf : 100 9 . 

 While this ratio was some 6 points below the norm, it differed by 

 only 4.4 points from the sex ratio .found in the 1510 litters ob- 

 tained by the mating of inbred females with -stock males (103.5 cf 

 : 100 9 ). The results as a whole, therefore, do not indicate that 

 the sex ratio was influenced to any extent by the fact that the 

 sires of the litters were inbred rather than outbred males. 



The final experiment to be made, the pairing of females from 

 the one inbred series with males from the other inbred series, was 

 not begun until the animals reached the twenty-sixth generation. 

 The number of litters as yet obtained is too small to afford a basis 

 for any general conclusion, but thus far females of the A series 

 (male line) when paired with males from the B series (female line) 

 have produced more male than female young, and, conversely, 

 females of the B series, when paired with males of the A series, 

 have shown a tendency to cast more female than male young. 



The results of these various series of experiments are summar- 

 ized and discussed in the following section. 



