Fig. 5. Hematocrits and blood cell counts of embryos or adult mice with the indicated genotypes. For adult mice (≥4 weeks old), white blood cell numbers (A), red blood cell numbers (B) and hematocrits (C and E) were machine scored by a Hemavet 3700R counter. For embryos (D and E), blood samples were acquired using 2 µl glass micropipettes and then briefly centrifuged to measure hematocrits. N, total number of mice used for the experiment. H × Stat5a/b^–/– indicates mice cross-breeding from Stat5a/b null mice with EpoR-H mice. (E) Numbers indicate days of gestation. The P values for all the comparisons support statistically significant differences in the hematocrits. To indicate the types of P values associated with the results, in (C) the two-tailed P values for the means of the various mutants relative to wild type are: H, 1.3 × 10^–3; HM, 8.0 × 10^–12; Stat5a/b, 6.4 × 10^–4; H/Stat5a/b, 9.2 × 10^–7.