Chromosome 15 (human)

Chromosome 15 (human)
Pair of human chromosome 15 (after G-banding). One is from mother, one is from father.
Chromosome 15 pair in human male karyogram.
Features
Length (bp)	101,991,189 bp
No. of genes	1,814 1,796
Type	Autosome
Centromere position	Acrocentric
Identifiers
RefSeq	NC_000015
GenBank	CM000677

Chromosome 15 is one of the 23 pairs of chromosomes in humans. People normally have two copies of this chromosome. Chromosome 15 spans about 101 million base pairs (the building material of DNA) and represents between 3% and 3.5% of the total DNA in cells.

Identifying genes on each chromosome is an active area of genetic research. Because researchers use different approaches to genome annotation their predictions of the number of genes on each chromosome varies. In January 2017, two estimates differed by 10%, with one estimate giving 1,814 genes, and the other estimate giving 1,796 genes.

The human leukocyte antigen gene for β2-microglobulin is found at chromosome 15. The following are some of the genes located on chromosome 15:

The following conditions are caused by mutations in chromosome 15. Two of the conditions (Angelman syndrome and Prader-Willi syndrome) involve a loss of gene activity in the same part of chromosome 15, the 15q11.2-q13.1 region. This discovery provided the first evidence in humans that something beyond genes could determine how the genes are expressed.

The main characteristics of Angelman syndrome are severe mental retardation, ataxia, lack of speech, and excessively happy demeanor. Angelman syndrome results from a loss of gene activity in a specific part of chromosome 15, the 15q11-q13 region. This region contains a gene called UBE3A that, when mutated or absent, likely causes the characteristic features of this condition. People normally have two copies of the UBE3A gene, one from each parent. Both copies of this gene are active in many of the body's tissues. In the brain, however, only the copy inherited from a person's mother (the maternal copy) is active. If the maternal copy is lost because of a chromosomal change or a gene mutation, a person will have no working copies of the UBE3A gene in the brain.

In most cases (about 70%), people with Angelman syndrome have a deletion in the maternal copy of chromosome 15. This chromosomal change deletes the region of chromosome 15 that includes the UBE3A gene. Because the copy of the UBE3A gene inherited from a person's father (the paternal copy) is normally inactive in the brain, a deletion in the maternal chromosome 15 results in no active copies of the UBE3A gene in the brain.