Myoblast lineages are heterogeneous. EGFP-expressing myoblasts were studied as in Figure 1. Differentiation medium (DM) was added ± IGF-I (R3-IGF-I (2 nM)), as indicated. (A, B) Line plots showing the number of cells derived from each lineage and the outcome (alive or dead) tracked on the y-axis. (C, D). Variation in outcomes of progeny for individual founder myoblasts leads to a shift in the population. The population number was normalized across time. Red, founder cells and their progeny with zero surviving myoblasts; green, founders with 1 to 2 survivors; blue, lineages with ≥3 survivors.