Autosome

An autosome is a chromosome that is not an allosome (i.e., not a sex chromosome). Autosomes appear in pairs whose members have the same form but which differ from other pairs in a diploid cell, whereas members of an allosome pair may differ from one another and thereby determine sex. For example, in humans there are typically 22 pairs of autosomes and one allosome pair. The allosome pair consists of two X chromosomes (female) or one X and one Y chromosome (male). (Atypically XYY, XXY, XXX, XXXX, XXXXX or XXYY, among other allosome combinations, are known to occur. These generally cause developmental abnormalities.) The autosome pairs are labeled with numbers (1-22 in humans), and allosomes are labeled with their letters.