Fig. 2. Blastocysts show distinctive clonal patterns. (A-D) Mouse embryos were analysed using the centres of gravity of the clones made up of the descendants of the 8-cell-stage blastomeres. (A) Merge of DIC and 3D representation of a blastocyst (colouring as in B). (B) Colours used to code for the 2- and 8-cell-stage descendants. MM and EE embryos were colour-coded by placing the first dividing cells in the left lineage. M, meridional second cleavage division (M1 and M2 being their daughters); E, equatorial second cleavage division; EA, EV, descendants of 4-cell blastomeres produced by equatorial division. A, animal; V, vegetal. (C) Determining the centre of gravity of each clone. The centroids (white dot) of the tetragons (white dotted lines) defined by the 8-cell-stage descendants were calculated (example shown for the blue clone). The coordinate of the mid-point of the embryonic-abembryonic boundary (red dot) was used to align an illustration of the cavity (white ellipse). (D) Scheme generated using the method described in C. Each dot represents the centre of gravity of a single 8-cell clone. The ellipse indicates cavity position and the dashed ellipse the outline of the embryo. (E-G) Schemes representing the three different groups of blastocysts. 8-cell clones (upper row) and 2-cell clones (lower row) use the colour code shown in B. The frequency of each group (%) is indicated (n=66). (E) Embryonic/abembryonic pattern. Arrowhead marks region #4. (F) `Half-half' pattern. The dashed line indicates the separation of the 2-cell-stage clones. (G) `Mixed' pattern. (H) Schematic embryonic/abembryonic pattern. Colour code as shown in B. Regions derived from one 2-cell-stage blastomere are positioned in the embryonic part (left). One region reaches slightly into the abembryonic part (asterisk). Three regions of the other 2-cell-stage blastomere are positioned in the abembryonic part (right) - one region (`region #4'/`dovetailed region') is positioned in the embryonic part (#4). The embryonic-abembryonic boundary is indicated by the dashed line. The presence of region #4 might explain the shift of this axis (red arrow; black line).