Figure 1.

Structural organization of the human, caiman, and African clawed toad amelogenin genes. Exons, indicated by boxes, are numbered 1–7, and the numbers below exons indicate the length in base pairs. The variable length of human X and Y exons is indicated by two numbers separated by a slash. Exons known to be alternatively spliced are indicated by hatched boxes. The first exon–intron boundary in the toad amelogenin genes has not been identified.