GATA1 plays a critical role in differentiation, proliferation, and apoptosis during erythropoiesis. We developed a Gata1 knock-down allele (Gata1.05) that results in GATA1 expression at 5% of endogenous level. In female mice heterozygous for both the Gata1.05 and wild-type alleles, we observed a predisposition to erythroblastic leukemia three to six months after birth. Since no male Gata1.05 progeny survive gestation, we originally maintained heterozygous females in a mixed genetic background of C57BL/6J and DBA/2 strains. Around 30% of these mice reproducibly develop leukemia, but the other subset did not develop leukemia, even though they harbor a high number of preleukemic erythroblasts. These observations prompted us to hypothesize that there may be potential influence of genetic determinants on the progression of Gata1.05-driven hematopoietic precursors to full-blown leukemia. In an initial examination of Gata1.05/X mice backcrossed into C3H/He, BALB/c, DBA/2, C57BL/6J and 129X1/SvJ strains, we discerned that the backgrounds of C57BL/6J and 129X1/SvJ significantly expedited leukemia onset in Gata1.05/X mice. Conversely, backgrounds of C3H/He, BALB/c and DBA/2 did not substantially modify the effect of the Gata1 mutation. This indicates the existence of genetic modifiers that accentuate Gata1.05 leukemogenesis. Subsequent cohort studies evaluated Gata1.05/X mice within mix backgrounds of BALB/c:129X1/SvJ and BALB/c:C57BL/6J. In these settings, Gata1.05-driven leukemia manifested in autosomal dominant patterns within the 129X1/SvJ background and in autosomal recessive patterns within C57BL/6J background. To the best of our knowledge, this study provides the inaugural evidence of genetic modifiers that can reshape the outcome based on leukemia-associated gene signatures.