Fig. (6) ABCB1. Genetic polymorphisms in the ABC family. The human ABCB1 (ATP-binding cassette transporter B1) gene is located on chromosome 7 at q21.1and consists of 29 exons numbered from -1 to 28. Here shown in the figure are 1 to 28, two promoter regions are at -1 and 1, however research has also found that the actual translation site starts at 2 and the coding sequence consists of 26 exons, 2 to 28.