BECK, S.L.: Skeletal Variation By “Batch” Among CD-1 Mice Reveals Continuing Genetic Heterogeneity.

The random-bred CD-1 mouse is widely favored as a test organism by regulatory agencies, pharmaceutical houses, among others, because of their broad array of genotypes, mimicing the human population. There is, therefore, concern about their continuous genetic heterogeneity. We purchased 7 groups of CD-1 mice from the same supplier, over a period of several years. The present study compares untreated controls from these 7 “batches”;, at 60-65 days post natal, for 88 normally-occurring skeletal variants. Most of the skeletal variants examined each strain-specific values among inbred strains and so are a good indicator of variation. There was significant (P<0.01) variation between groups among 63 variants. Seventeen variants never appeared, and 9 occurred in only 1 specimen in all 7 groups (686 mice). High variability among all groups was seen for 10 variants. Average number of variants for each group that differ in 2-way comparisons with each of the others, and ranges, are: G1 = 21 / 16-26, G2 = 18.2 / 16-23, G3 = 20 / 16-23, G4 = 16.7 / 10-26, G5 = 13.8 / 9-19, G6 = 16.5 / 9-25, G7 = 16.2 / 13-22. The variants showing the largest number of significant comparisons were doubled Mandibular Foramen (18 of 21 possible comparisons), doubled Foramen Pterygoideus (15), imperfect Transverse Foramen on cervical vertebra (CV) 7 (15), Arch Foramen CV5 (15), Parted Frontal bones (14), Malformed Sternebrae (14), anteriad suture on posterior border of the Palatine bone (14), perforated Fossa Olecrani of the humerus (13), and caudalized Sacral Vertebra 3 (12). The sizeable number of variants which differ significantly in these 7 groups of CD-1 mice purchased over a period of several years suggest that these animals continue to be morphologically diverse. (Supported by the Department of Biological Sciences and the University Research Council of DePaul University).