EFFECTS OF INBREEDING AND CROSSBREEDING. 



Table 2. — The supmority (+) or inferiority ( — ) of the record of each experiment to that 

 made by the inbred stock at the same time. 



JWith respect to the first three characteristics (percentage born alive, percentage raised of those born aUve, 

 and percentage raised) the difference from the record of the inbred stock is corrected as described in the 

 text. With respect to the other characteristics, the differences are given as percentages of the record of 

 the inbred stock.] 



Experi- 

 ment. 



Percent 

 bom 

 alive. 



Percent 



raised 



of those 



born 



alive. 



Percent 

 raised. 



Birth 

 weight, 

 total. 



Birth 

 weight, 



those 

 raised. 



Gain. 



Weight 



at 

 33 days. 



Size 



of 



litter. 



Litters 

 per 

 year. 



Young 

 per 

 year. 



Young 



raised 



per 



year. 



2 



-3.8 

 -1.4 

 +2.3 

 +0.7 

 +4.3 

 + 1.0 



+3.3 

 -1.5 

 -6.0 

 +4.3 

 -5.3 

 -1.6 



-0.3 

 -2.8 

 -2.3 

 +3.3 

 -0.4 

 -1.6 



-9.4 

 +3.4 

 +2.3 

 +5.8 

 -4.6 

 +2.8 



-7.7 

 +6.1 

 +0.8 

 +4.6 

 -5.2 

 + 1.6 



-18.6 

 +13.2 

 +0.3 

 +11.8 

 -1.1 

 +0.6 



-14.4 

 + 10.4 

 +0.4 

 + 9.0 

 -2.6 

 +1.0 



-3.6 

 +7.8 

 -6.5 

 +4.2 

 + 1.0 

 -1.6 



+12.9 







+1.5 



+9.7 



-8.4 



-11.9 



+8.8 

 +7.8 

 -5.1 



+ 14.3 

 -7.5 



-13.3 



+13.1 



13 



+2.1 



32 . 



— 7.8 



35 



+16.1 



39 



-11.9 



Other 



-15.2 



CO... . 



+0.5 

 + 2.7 

 +7.6 

 + 6.9 

 + 9.0 

 + 3.8 

 + 9.8 

 +5.1 

 +8.6 



+ 11.2 



+ 12.4 



+ 11.8 



+ 12.0 



+ 9.3 



+ 7.9 



+4.8 



+ 5.9 



+ 10.8 



+9.2 

 + 10.4 

 + 14.7 

 + 14.6 

 + 13.9 



+ 8.9 

 + 11.5 



+8.8 

 + 14.9 



+ 1.7 



+3.6 



+8.8 



+ 12.9 



+ 10.7 



+ 6.7 



+ 8.3 



+8.0 



+ 10.8 



+2.5 

 +3.6 

 +8.1 

 +9.2 



+7.1 

 +4.5 

 +4.5 

 +8.4 

 +9.4 



+ 13.2 

 +11.7 

 + 11.9 

 +21.0 

 +15.9 

 + 12.7 

 +21.7 

 + 19.5 

 + 18.9 



+ 9.0 

 +8.6 

 +10.5 

 + 16.5 

 + 12.5 

 + 9.8 

 + 15.3 

 + 15.3 

 + 15.2 



-1.8 

 +3.6 

 +28.3 

 + 14.3 

 + 10.2 

 +4.0 

 + 14.2 

 + 15.1 

 + 14.0 



+0.8 

 +19.4 



+9.3 

 +36.1 

 +33.3 

 +25.0 

 + 17.8 

 +27.0 

 +14.1 



-1.0 



+23.6 

 +40.2 

 +55.4 

 +46.9 

 +29.9 

 + 34.5 

 +46.1 

 +30.1 



+9.5 



•CA 



+47.4 



AC 



+63.7 



CC 



+ 82.5 



CI 



C2.. 



+73.1 

 +43.7 



CL 



+56.2 



CG... 



+53.4 



B 



+60.2 







/CO 



/4-0 



The actual differences are shown in Table 30. In Table 2 the 

 differences in the case of the weights and fertility are shown as per- 

 centages of the record of the total inbred stock. Experiment B, for 

 example, produced litters 14 per cent larger than the inbreds. In 

 the case of the mortality data, the actual differences shown in Table 

 29 are modified to allow for the influence of different basic percentages 

 in the inbred stock. To illustrate, 69.4 per cent was the percentage of 

 the inbreds raised to 

 33 days while Experi- 

 ment AC was in pro- 

 gress. Only 58.9 per 

 cent were being raised 

 simultaneously with 

 CC. There is more 

 room for improvement 

 in the latter case. 

 Thus the 8.2 per cent 

 advance of AC beyond 

 the inbreds may mean 

 as much as the ad- 

 vance of 11.9 per cent shown byCC. A correction has been applied 

 according to the method described in a previous paper (Wright, 1920)* 

 in connection with the percentage of white in the coats of guinea pigs . 

 Assume that the distribution of the animals in a given stock relative 

 to conditions which make for survival or death follows approximately 

 a normal probability curve. The area to one side of a certain ordi- 



< See "Literature cited" at end of bulletin. 

 6448— 22— Bull. 1121 2 





y-j ■s'Tg 7-s /a-/^yi9 4-^ p^ x>-/2, /-3 4^ 7-9 /0-iz , /-J' 'f-is y-s /0-/2, 

 7^7s /&/7' /s>/s /9/9 



Fig. 7.— The sex ratio (number of males per 100 females) among the 

 young born in the inbred stock during successive 3-month periods, 

 1916-1919. 



