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Genetic control of juvenile growth rate in mice: variation between a congenic strain and its background strain.

Studies on the genetic regulation of growth are confounded by the multigenic basis of growth. There is a need to isolate simplified genetic systems for the study of growth. We compared two closely related mouse strains and their F1 hybrids with regard to birth and weaning weights. The strains we used were C57BL/6 (B6) and a congenic derivative of B6 (HW54) that contains a short segment of BALB/c chromosome 7 spanning the H-24 and Gpi-1 loci. Despite the genetic similarity of these strains, they differed significantly in both birth and weaning weights. At birth, B6 pups were on average as much as 6.6% heavier than were pups from HW54. By the time of weaning, this trend was reversed; HW54 pups were as much as 13.8% heavier than were B6 pups. (B6 x HW54)F1 hybrids were intermediate between the parental strains in birth weight but were identical to B6 animals at weaning. An analysis of the F2 generation suggested that postnatal growth differences between B6 and HW54 are probably dependent on the maternal genotype. These strain-specific growth rates result from polymorphism at a restricted portion of the genome and represent a highly simplified system for the study of the genetics of growth.