autosomes
In a given species, chromosomes can be identified by their number, size, centromere position, and banding pattern. In a human karyotype, autosomes or body chromosomes all of the nonsex chromosomes are generally organized in approximate order of size from largest chromosome 1 to smallest chromosome 22 . The X and Y chromosomes are not autosomes. However, chromosome 21 is actually shorter than chromosome 22. This was discovered after the naming of Down syndrome as trisomy 21, reflecting how this disease results from possessing one extra chromosome 21 three total . Not wanting to change the name of this important disease, chromosome 21 retained its numbering, despite describing the shortest set of chromosomes. The chromosome arms projecting from either end of the centromere may be designated as short or long, depending on their relative lengths. The short arm is abbreviated p for petite , whereas the long arm is abbreviated q because it follows p alphabetically . Each arm is further subdivided and denoted by a number. Using this naming system, locations on chromosomes can be described consistently in the scientific literature.