autosomal

An autosome is any chromosome that is not a sex chromosome. In humans, there are 22 pairs of autosomes and two sex chromosomes (X and Y). Autosomes occur in homologous pairs and carry the majority of a person’s genes. Because they are present in two copies in both males and females, autosomal genes contribute to traits and diseases that affect both sexes similarly. The designation autosomal contrasts with sex-linked chromosomes, whose inheritance depends on sex.

Autosomal inheritance describes how traits and disorders are transmitted via autosomes. Autosomal dominant conditions require only one copy of a mutant allele and typically affect males and females equally, with affected individuals often having an affected parent. Autosomal recessive conditions require two copies of the mutant allele; carriers are usually unaffected, and the trait can appear in siblings with unaffected parents. Both sexes are equally at risk. There are also variations such as incomplete dominance and codominance, as well as variable penetrance and expressivity, that shape how a trait presents.

Many genetic disorders involve autosomal genes. Examples of autosomal dominant disorders include Huntington disease and Marfan syndrome; autosomal recessive disorders include cystic fibrosis, sickle cell disease, and phenylketonuria. In addition to single-gene disorders, autosomal aneuploidies (such as trisomy 21, trisomy 18, and trisomy 13) reflect numerical abnormalities of autosomes and can have severe developmental consequences. Autosomal inheritance is a foundational concept in human genetics, informing diagnosis, counseling, and research.