A cartoon of the ALS gene family, with each gene depicted as a human figure. For the purpose of this illustration, each gene is considered to be made of three domains (e.g. a head, torso, and legs). The torso in each gene is a region of tandemly repeated DNA sequences, which can be many kilobases in length. Because there are many loci that contain these repeated sequences, assembly of the ALS genes using automated methods often fails. (Image by Kerry Helms, The Design Group @ Vet Med; published in Hoyer et al., 2008. Med Mycol 46:1-15).