Intron positions in the 100 most N-terminal amino acids of the coding sequence of eukaryotic genes. Genes are divided into the systematic groups vertebrates, arthropods, fungi, and flowering plants (Magnoliophyta). The data sets are homology reduced. Left: genes predicted to code for a protein with a signal peptide; right: genes predicted not to carry a signal peptide. For phase 0 introns the position refers to the amino acid after the intron.