Fig. 6. Distinguishable fates of blastomeres of the two-cell embryo. Confocal sections of a blastocyst showing that the clonal border between progeny of the two-cell blastomeres corresponds with a plane separating the embryonic and abembryonic parts. Blastomeres were labelled at the two-cell stage with dyes of different colours (Piotrowska et al., 2001). The boundary zone is marked with broken red lines and the border of the blastocoel was traced on a central section and is shown projected onto each of the other sections as a broken white line. (A-H) Individual optical sections at 7.5 µm intervals in the ‘z-dimension’. There is a tilt of the clonal border that can be seen in the ‘z-dimension’ of this series of micrographs. Scale bar: 20 µm.