A "package" of DNA that holds the genetic code to life. In humans, each non-sex cell has 23 pairs of chromosomes.

A chromosome is one of the "packages" of DNA in the nucleus of a cell. Genes are DNA units housed on chromosomes, like beads on a string. It is from these genes that the RNA is made, which in turn is the template for making proteins. A chromosome is mainly composed of DNA, but it can also be associated with "packaging" proteins, called histones, and others. Humans have 23 pairs of chromosomes (22 pairs of autosomes and one pair of sex chromosomes). Because each biological parent contributes one chromosome from each pair to their child, each child inherits half of their chromosomes from their mother and half from their father. This is important for understanding the difference between recessive, dominant and X-linked inherited retinal degenerative diseases (see individual definitions).