Figure 6. Analysis of secondary lineage 4-cell clones.

A) There are seventy different possible arrangements of 4 labeled cells in 8. They are presented here ordered from most dispersed (perfect alternation between labeled and unlabeled cells) at the top to least dispersed (4 labeled cells next to 4 unlabeled cells) at the bottom. If intercalation is completely random, then all 70 of these arrangements should be equally likely. The histogram indicates how often these different arrangements of labeled cells were actually observed among the 152 secondary 4-cell clones we imaged. B) 4-cell secondary clone on the left side of the embryo. The secondary lineage is slower to undergo the final division than the primary lineage, so there has already been some intercalation in the primary lineage. The cartoon diagram indicates the relative frequency of different patterns of intercalation detected.