Individual SSCs consistently give rise to SSCs and differentiating germ cells independently of environmental cues. (A) Cultures of single germ cells from two randomly selected long-lasting clones (Nos. 1 and 6) derived from single SSCs showed that they contained 82.7% and 78.4% mortal differentiating cells and 17.3% and 21.6% immortal SSCs, respectively (n = 84). This was similar to their parent cell line (82.7% differentiating and 17.3% SSC, n = 84), which indicates that individual SSCs consistently give rise to both SSCs and differentiating germ cells. (B) Schematic diagram based on the long-term time-lapse imaging of twin daughter cells of a single SSC that gave rise to two clones with different fates. In one clone, all cells died synchronously by day 10, whereas the other continued to live by day 18, which indicates that one of the twin daughter cells differentiated, whereas the other became an SSC. (C and D) Relative positions of the two daughter cells during the time between their birth and next division (Video 3). (C) The solid line indicates the mean diameter (∼13 µm) of the two cells, and black dots mark the distance between the geometric centers of the two cells at the indicated time points. (D) Centroid positions of each daughter cell during the time window are represented by the centers of the red and blue circles, respectively. The diameter of the circles is equal to the mean diameter of the cells to show the area transiently visited by the two cells.