Competitive disadvantage for

Sca-1^−/− bone marrow compared withSca-1^+/+ bone marrow.Sca-1^+/+(Gpi1AA) andSca-1^−/−(Gpi1BB) bone marrows were mixed at specific ratios and used to repopulate lethally irradiated mice. The x-axis represents input Sca-1^+/+cells (Gpi1AA), and the y-axis represents output Sca-1^+/+(Gpi1AA) cells. If there is no difference in the ability of HSCs to repopulate irradiated mice, the output percentage of Gpi1AA cells will be the same as the input percentage (solid line, or predicted values). In control experiments, Sca-1^+/+Gpi1AA bone marrow was mixed with Sca-1^+/+Gpi1BB bone marrow and used to repopulate lethally irradiated Gpi1AA mice. These results (square dotted line) reflect the expected result that there is no competitive advantage for either bone marrow population. The experimental results (dashed and round dotted lines) demonstrate that Sca-1^−/−bone marrow has a competitive disadvantage compared with Sca-1^+/+cells. The dashed and round dotted lines representSca-1^+/+Gpi1AA mice orSca-1^−/−mice, respectively, as transplant recipients.