Numbers, n, of marrow eLTRC surviving irradiation plotted as a function of dose. Because of the break in the curve below 3.5 Gy, the regression line was fitted by least-squares method to data points from 3.5 to 6.5 Gy. Correction of observed n at the 7.0-Gy dose was done as for blood samples. Negative inverse of the slope or D₀ was calculated to be 0.83 Gy ± 0.31 Gy (mean ± SE). The y-intercept or total number of eLTRC per mouse was calculated to be 11,863, +46,070, −9,434 cells (mean ± SE).