Autosom

An autosom, or autosome, is any chromosome that is not a sex chromosome. In humans and many other organisms, autosomes exist as homologous pairs in diploid cells. They are numbered 1 through 22 in humans, while the sex chromosomes comprise the remaining pair (XX in females, XY in males).

Autosomes carry the vast majority of genetic material and encode genes involved in a wide range of cellular functions and traits, not directly determining an organism's sex. While some genes on the sex chromosomes influence sexual characteristics, autosomal genes affect development, metabolism, and disease susceptibility across sexes.

Inheritance of autosomal traits follows Mendelian patterns, most commonly autosomal dominant and autosomal recessive. Affected individuals with an autosomal dominant condition usually have one copy of the mutated allele; autosomal recessive conditions require two copies. Examples include Huntington's disease (autosomal dominant) and cystic fibrosis (autosomal recessive).

Autosomal aneuploidy can occur when chromosomes fail to segregate during meiosis. Such conditions include Down syndrome (trisomy 21), Edwards syndrome (trisomy 18), and Patau syndrome (trisomy 13).

Across species, the exact number of autosomes varies; the term autosome refers to non-sex chromosomes regardless of count. Modern genomics continues to map and characterize the genes carried on autosomes and their roles in health and disease.