Humans have two dozen chromosomes in there cell nuclei. The two dozen chromosomes are designated XY and 1 to 22. These two dozen chromosomes are also grouped into sizes designated A to G. The first two size groups A and B consist of 5 chromosomes. These first five chromosomes are shown here. The DNA molecule of a chromosome runs it’s length and accounts for the banding shown. 5q2.3.1 in chart locates chromosome 5, “q” long-arm, region 2, band 3, sub-band 1. This is a locus DNA at this location.