Contributions of tissues to expression of a major gene for growth in chimeric mice

The objective of this research was to determine the effect of genotype of particular tissues and organs on the growth of a chimera produced by aggregating an embryo homozygous for the high-growth (hg) allele with an embryo from a control line of wild-type mice lacking the deletion responsible for the high-growth phenotype. A total of 107 chimeric mice were produced, 81 males and 26 females. The preponderance of male chimeras closely fit the expected 3:1 ratio of males to females in balanced chimeric populations, suggesting that neither of the two genetic lines appeared to have a selective advantage for contributions to chimeric tissues. No single correlation between individual tissue chimerism and mouse growth was remarkable relative to correlations of chimerism of other tissues to growth. Other statistical models, including multiple regression techniques, did nothing to identify particular organs, tissues or various combinations that improved the explanation of expression of the high-growth phenotype by percentage of high-growth cells in that organ. These observations suggest that the chromosomal deletion thought to cause the high-growth phenotype has a systemic effect, without dominant effects of or on individual organs or tissues; the precise mechanism has yet to be determined.