X chromosome. Computer artwork showing a human X chromosome, one of the two sex chromosomes. The red regions mark out the telomeres, structures which protect the ends of the chromosome and may play a key role in cell aging. A chromosome is made up of DNA (deoxyribonucleic acid) and it carries the inherited characteristics of a human in the form of genes. The banding patterns created by staining the chromosome are represented by blue dots. Each type of chromosome can be identified by a unique banding pattern. Most human cells contain 46 chromosomes of which one pair are the sex chromosomes. A female has two X chromosomes and a male has one X and one Y chromosome.