Mutation in c-Myb ameliorates thrombocytopenia in Bcl-x mutant mice. Platelet counts in wild-type mice (c-Myb^+/+Bcl-x^+/+) or mice homozygous for the Plt20 allele of Bcl-x (Plt20/Plt20) and wild-type (+/+), heterozygous (Plt4/+), or homozygous (Plt4/Plt4) for the c-Myb^Plt4 allele. The mean ± SD of platelet counts from 4 to 14 mice per genotype are shown. *P < .05 in Student t test for comparison of data from c-Myb^Plt4/Plt4 Bcl-x^Plt20/Plt20 mice with that of c-Myb^+/+Bcl-x ^Plt20/Plt20 controls.