(A) We quantified HSC frequencies of WT, Mpl^–/–, Lnk^–/–, and Mpl^–/–Lnk^–/– mice using limiting dilution cBMT. Results are pooled from 3–5 independent experiments. (B) Top: BM cells from WT, Mpl^–/–, Lnk^–/–, and Mpl^–/–Lnk^–/– mice were mixed at 1:1 ratio with CD45.1 competitor cells and transplanted into irradiated recipient mice. Chimerisms of transplanted mice were measured 1, 4, and 8 months after transplant (mean ± SD). n = 10. Middle panel: Transplant results from WT, Mpl^–/–, and Mpl^–/–Lnk^–/– mice when mixed at 9:1 ratio with the competitors. Bottom: Transplant results from Lnk^–/– BM cells when mixed at different ratios with the competitors. n = 5. *P < 0.005, WT compared with Mpl^–/–Lnk^–/– at the same time points, 2-tailed unequal variance t test; ^#P < 0.005, compared with same strain at 4 months, 2-tailed paired t test; **P < 0.05, compared with same strain at 4 months, 2-tailed paired t test. (C and D) Primary transplanted mice were sacrificed at 8 months and total BM cells were transplanted into secondary recipients. (C) Transplant results from WT, Mpl^–/–, and Mpl^–/–Lnk^–/– mice when mixed at 9:1 ratio and Lnk^–/– mice when mixed at 1:19 ratio with the competitors. (D) Transplant results from WT, Mpl^–/–, and Mpl^–/–Lnk^–/– mice when mixed at 3:1 ratio and Lnk^–/– mice when mixed at 1:99 ratio with the competitors. Chimerisms of the primary transplanted mice (mean ± SD) are shown in the left panels and those of the secondary transplant (mean ± SEM) are shown in the right panels. **P < 0.05; ^†P = not significant, n = 5.