JAK2^V617F transgenic mice have enlarged spleens. Graphic representation of spleen weights of control and transgenic mice (11-12 weeks old except for Tg C, which was 4 weeks old). Error bars denote SD (n = 7, except for the Tg C bar, which represents only one sample). P values obtained from t tests are indicated. The weights of spleens range from 53 to 96 mg for control mice, 90 to 410 for transgenic line A (Tg A), and 68 to 117 for transgenic line B.