Influence of Maternal Phenotype on Metabolic Differentiation of Agouti Locus Mutants in the Mouse

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The results of extensive breeding experiments indicate that the phenotypic differentiation of embryos carrying the viable yellow, A vy, or mottled, am, mutations is influenced to a major extent by the agouti locus genotype and the strain genome of the dam. The Avy/a and am/a genotypes are each expressed in a spectrum of coat color phenotypes. These can be grouped into two classes, mottled and pseudoagouti.—In a reciprocal cross of C57BL/6JNIcrWf and AM/Wf-am/am mice, 29.5% of the offspring of C57BL/6 dams were of the pseudoagouti phenotype, whereas no pseudoagouti offspring were produced by AM strain dams.—Mottled yellow Avy/a mice become obese and tumor formation is enhanced in these mice in comparison with the lean pseudoagouti Avy/a siblings.—In two different reciprocal crosses using four different inbred strains, the proportion of pseudoagouti Avy/a offspring differed according to the strain of the dam. Regardless of strain, mottled yellow A vy/a dams produced significantly fewer pseudoagouti A vy/a offspring than did black a/a dams.—The data suggest that metabolic differentiation of Avy/a zygotes into phenotypic classes with different susceptibilities to obesity and tumor formation is influenced to a considerable degree by the metabolic characteristics of the oviductal and uterine environment of the dam.

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