Fig 1.
The accumulation of mutant clones in the wall of the small intestine of mice that received a daily i.p. injection of either 1 or 3 mg/kg ENU (7). The mice carried one copy of Dlb-1b, which codes for a stainable cell-surface lectin, and that allowed microscopic measurement of the frequency of unstainable, mutant sectors (clones) in the epithelium. The points show the observed frequency of mutant sectors during treatment (filled circles) and after treatment ceased (open circles). The curves show the expected values if the frequency of sectors equals 3.3 × 10−6 × (mg/kg ENU) × (weeks)2. To allow for the time between mutation in a cell and the appearance of a visible clone of mutant descendants, the points were displaced 4 days to the left (7). The raw data for this figure were kindly provided by John Heddle (York University, Toronto).