. The effects of inbreeding and crossbreeding on guinea pigs : III. crosses between highly inbred families. the other characters. For the last namedthere is something like one-eighth determination by the young. One result which seemed rather puzzling was the relatively lowrecord of Experiment CG, in which the parents were selected as ex- ErFECTS OF IXBREEDIXG AND CROSSBREEDIXG. 47 ceptionally heavy and vigorous at weaning. In this case, as in CL,matings were made at random as far as ancestry was concerned. Inmany cases the same family enters into the ancestry of both parentsof a given animal i
. The effects of inbreeding and crossbreeding on guinea pigs : III. crosses between highly inbred families. the other characters. For the last namedthere is something like one-eighth determination by the young. One result which seemed rather puzzling was the relatively lowrecord of Experiment CG, in which the parents were selected as ex- ErFECTS OF IXBREEDIXG AND CROSSBREEDIXG. 47 ceptionally heavy and vigorous at weaning. In this case, as in CL,matings were made at random as far as ancestry was concerned. Inmany cases the same family enters into the ancestry of both parentsof a given animal in these experiments. For this reason, as we havejust seen, a lower record is to be expected than in Experiment CC,in which no family was used twice. SUMMARY AND GENERAL CONCLUSIONS. The Bureau of Animal Industry has conducted experiments tor 15years on the effects of inbreeding on guinea pigs. About 34,000animals have been recorded. These include the records of 23 sepa-rate families, each descended from an original pair exclusively bymatings of brother with sister (over 25,000 animals), a control stock. Fig. 27.—The vigor under crossbreeding (COj and under rene^^ed inbreeding (Cl, C2, C3, etc.) relative tothat in the iabred stock (X) and under continued crossbreeding (CC). Characters depending in variousdegrees I-V) on dam Tor sire) and young. in which inbreeding has been carefully avoided (over 4,000 animals),and crosses among the inbred families ^nearly 5,000 animals). The fact that inbreeding of the closest possible kind has been car-ried on for over 20 generations in several families, without any veryobvious degeneration, is a noteworthy result. There has been on the average, however, a decline in all elements ofvigor. The mortality at birth and between birth and weaning, theweight at various ages, the regularity in producing litters, the size01 litter and the resistance to tuberculosis are the principal character-istics v>hich have been studied in this connection. FuU
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Keywords: ., bookauthorwrightse, bookcentury1900, bookdecade1920, bookyear1922
