Fig. 7. Bst causes a growth disadvantage in vivo. (A) Chimera analysis protocol. Exactly five or ten R26 ES cells were injected into mutant and control blastocysts. (B) Coat color comparison of adult chimeras. Rpl24 genotypes were determined by allele-specific PCR. C57BLKS and R26 contributions were determined by the percent black (a/a) and agouti (A/A) coloration, respectively. The R26 contribution was significantly greater in chimeras derived from Bst/+ blastocysts, in experiments where five (left) or ten (right) ES cells were injected (P<0.01, Mann-Whitney nonparametric rank sum tests). Open and closed symbols represent female and male chimeras, respectively. (C) Typical Bst/+ and +/+ chimeras showing 50% and 5% agouti coats, respectively (ten ES cell injection). (D) ß-Galactosidase staining of cryopreserved tissues from chimeras in (C). The increased R26 contribution (lacZ positive) in Bst/+ chimeras is evident in all tissues examined. Scale bars: 150 µm.