Figure 2.

Transcripts of Hox cluster genes and the Brachyury gene, per embryo or larva. Histograms indicate transcript numbers for the indicated stages of embryogenesis: 0 h, unfertilized eggs; 6 h, early gastrula; 12 h, swimming prototrochophore; 24 h, L1 larva; and 48 h, L2 larva. The dots indicate the number of cells per organism (same ordinates). Each panel represents a single data set. Transcript numbers were calculated from the slopes as described (ref. 25; see Fig. 1), taking into account the amount of total RNA per embryo (6.5 ng; see Materials and Methods) and the lengths and specific activities of the probes. Hox probes are from Irvine and Martindale (21); the Brachyury probe is described in Materials and Methods.