. The effects of inbreeding and crossbreeding on guinea pigs : III. crosses between highly inbred families. g experiments. Males. Females. Experiment. Num-ber. Weight(grams). Num-ber. Weight(grams). Inbreds (in CO, AC, CA) 95 779 776 ± ± ± 91829 641 ± CO (in CC, CI, CA, AC) 726 ± Cl (in C2).. .. . 667 ± EFFECTS OF IXBREEDIXG AXD CEOSSBREEDIXG. 25 It will be seen that the first cross (CO) results in an increase of 12or 13 per cent in adult weight, but that at least half of this is lost /O Is /3 CO 3/?/9AfS^865,^726 / \ \ / / > \ C/ 35 3/^ A / 3776,^64/— 3a / ^ 2 Fj
. The effects of inbreeding and crossbreeding on guinea pigs : III. crosses between highly inbred families. g experiments. Males. Females. Experiment. Num-ber. Weight(grams). Num-ber. Weight(grams). Inbreds (in CO, AC, CA) 95 779 776 ± ± ± 91829 641 ± CO (in CC, CI, CA, AC) 726 ± Cl (in C2).. .. . 667 ± EFFECTS OF IXBREEDIXG AXD CEOSSBREEDIXG. 25 It will be seen that the first cross (CO) results in an increase of 12or 13 per cent in adult weight, but that at least half of this is lost /O Is /3 CO 3/?/9AfS^865,^726 / \ \ / / > \ C/ 35 3/^ A / 3776,^64/— 3a / ^ 2 Fjg. 15.—Adult weight, 1917-1920. Comparison between inbred families (2, 13, 32, 35, 39), total inbreds{\), random-bred stock (B), first cross (CO), and first generation of renewed inbreeding (CI). Percentagedifferences for males and females averaged. (See Table 9.) on renewing inbreeding (Cl). Figure 15 brings out these points graphically. FREQUENCY OF LITTERS. It is conceivable that the heredity of the fetuses might make adifference in the number of litters completely absorbed or aborted at. 20 Tig. 16.—Regularity in producing litters (litters per mating per year), 1916-1919. Efiects of seasonal con-ditions eliminated (Table 2). (See Fig. 8 for explanation of symbols.) an early stage, and thus make a difference in the frequency of recordedlitters. As it turns out, however, the frequency of Utter (Fig. 16) is6448—22—Bull. 1121 i 26 BULLETIN 1121, U. S. DEPARTMENT OF AGRICULTUEE. virtually identical in the cases of inbred females mated respectivelywith brothers (young inbred) and with unrelated inbred naales (CO). When the crossbred young themselves become parents there isa marked increase in the regularity with which litters appear. Theresult is practically the same whether these crossbred parents areunrelated (CC) or brother and sister (Cl), again indicating thatthe vigor or weakness of the young is not a factor. A falling offappears when the parents are from th
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