What characteristic distinguishes one chromosome from another?

Chromosomes differ in their structure, shape and size.

The karyotype is the complete set of individuals chromosome complement (snapshot of an individual's chromosomes). The process of pairing and ordering all the chromosomes is known as karyotyping. Each chromosome pair in a karyotype has its own distinct "barcode" of bands. Cytologists (who do the karyotyping) have developed stains that bind with DNA and generate characteristic banding patterns for different chromosomes. For example, Adenine-Thymine (A-T) rich regions of DNA, stain more darkly comparing to Guanine-Cytosine (G-C) regions (Gimsa dye). Different chromosomal staining techniques show variations in chromosome structure and thus differences between chromosomes.