NCX Gene Homologs and Localization. Teleost, amphibian and aves list of NCX genes and localization with scaled distances in between exons. Open rectangles represent the exons at the N-terminus located before the alternative spliced exons and the dashed rectangles represent the exons after the alternative spliced exons at the C-terminus. Alternative exons A (black), B (light grey) and the rest of the cassette exons (dark grey) are shown where it is applicable. NCX duplicate genes are separated with NCXa and NCXb at the top and bottom of the list, respectively.