Which chromosome type includes human chromosomes 1 through 22?

Human chromosomes 1 through 22 are autosomes. In humans, these 22 numbered chromosome types are the non-sex chromosomes, while the X and Y chromosomes are the sex chromosomes, also called allosomes.

Most human body cells contain two copies of each autosome—one inherited from each parent—for 44 autosomal chromosomes altogether. The chromosome numbers were assigned broadly by size, with chromosome 1 the largest and chromosome 22 among the smallest, although chromosome 21 is actually slightly smaller than chromosome 22.

A common mix-up is treating “autosome” as meaning a chromosome unrelated to sex determination. Autosomes are not the sex chromosomes, but they can carry genes that influence sexual development. For example, SOX9 is located on chromosome 17 and plays an important role in sex development.

Eggs and sperm normally contain one copy of each autosome, whereas ordinary diploid cells contain pairs. That distinction helps explain why an extra copy of an autosome, such as chromosome 21 in Down syndrome, can affect development.