Possible Patterns of Differentiation in the Primitive Ectoderm of C3H/HeNBALB/cA Chimeric Blastocysts: An Inference from Quantitative Analysis of Coat‐Color Patterns

Abstract

Coat‐color patterns of 20 C3H/HeN++BALB/cA chimeras produced by using the same colony of mice in a series of experiments, were quantitatively analyzed, by means of a video‐image analysis system developed by Tachi (1988, 1989). In those chimeras, proportion of the two allogeneic components, i.e., C3H/HeN and BALB/cA, was relatively well balanced between the right and the left halves of the pelts, whereas between the anterior and the posterior regions it was unbalanced in favor of BALB/cA components in the anterior region. To interpret the results, a computerized geometrical model intended to simulate the hypothetical conditions of chimeric germ layers during early embryogenesis, was constructed. From the model, it was proposed that the seemingly high selection pressure for the BALB/cA components in the anterior region of this particular group of chimeras, might have been caused because the initial steps of the determination of the cranio‐caudal axis took place in the regions of the primary ectoderm where BALB/cA, rather than C3H/HeN blastomeres were predominant. Possible variations in the alleles of the genes regulating the germ layer differentiation, might conceivably be the cause for the observed tendencies.