Gene dosage

[2] The normal gene dosage is dependent on the species; humans generally have two doses -- one copy from the mother and one from the father.

[1] Ploidy refers to the number of complete sets of chromosomes in a cell.

For example, the gene that codes for the beta-subunit of hemoglobin (HBB) is located on chromosome 11.

Though not fully understood, it is thought that the increased expression of genes on chromosome 21 is the cause of some of the characteristic traits of Down syndrome.

Prokaryotes reproduce through asexual reproduction, usually by binary fission.

The genes that are closer to the origin site are replicated first and are consequently present in two copies in the cell for a longer time than the genes that are closer to the termination site.

Micrographic karyogram of a human male. Shows 2 sets of the 22 autosomal chromosomes and the 23rd chromosome set with one X and one Y.
Schematic karyogram of a human, showing an overview of the human genome , with 22 homologous chromosomes , both the female (XX) and male (XY) versions of the sex chromosome (bottom right), as well as the mitochondrial genome (to scale at bottom left).
Further information: Karyotype