In such organisms, meiosis creates gamete cells (eggs or sperm) having only one set of chromosomes.

Autosomal trisomies are described by referencing the specific chromosome that has an extra copy.

[citation needed] Thus, for example, the presence of an extra chromosome 21, which is found in Down syndrome, is called trisomy 21.

In rare cases, a fetus with Trisomy 13 can survive, giving rise to Patau syndrome.

Autosomal trisomy can be associated with birth defects, intellectual disability and shortened life.