XK and CYBB are neighboring genes. A. Idiogram of human chromosome X at 550 banding resolution. The bar indicates the location XK and CYBB genes and is expanded below to show the genomic region. B. Genomic context of Xp21.1. The region of chromosome X from 37,500 to 37,700 K is shown. Arrows indicate the location of the XK and CYBB genes. Numbering is based upon GenBank accession number NC_000023.10.