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 p articular tissues and organs on the growth of a chimera produced by aggrega ting an embryo homozygous for the high-growth (hg) allele with an embryo fr om a control line of wild-type mice lacking the deletion responsible for th e high-growth phenotype. A total of 107 chimeric mice were produced, 81 mal es and 26 females. The preponderance of male chimeras closely fit the expec ted 3:1 ratio of males to females in balanced chimeric populations, suggest ing that neither of the two genetic lines appeared to have a selective adva ntage for contributions to chimeric tissues. No single correlation between individual tissue chimerism and mouse growth was remarkable relative to cor relations of chimerism of other tissues to growth. Other statistical models , including multiple regression techniques, did nothing to identify particu lar organs, tissues or various combinations that improved the explanation o f expression of the high-growth phenotype by percentage of high-growth cell s in that organ. These observations suggest that the chromosomal deletion t hought to cause the high-growth phenotype has a systemic effect, without do minant effects of or on individual organs or tissues; the precise mechanism has yet to be determined.