Humans normally have 46 chromosomes in each cell, divided into 23 pairs. Two copies of chromosome 18, one copy inherited from each parent, form one of the pairs. Chromosome 18 spans about 78 million DNA building blocks (base pairs) and represents approximately 2.5 percent of the total DNA in cells.
Identifying genes on each chromosome is an active area of genetic research. Because researchers use different approaches to predict the number of genes on each chromosome, the estimated number of genes varies. Chromosome 18 likely contains 200 to 300 genes that provide instructions for making proteins. These proteins perform a variety of different roles in the body.
Related Genetics Topics
- Trisomy 18 — MedlinePlus Genetics
- Tetrasomy 18p — MedlinePlus Genetics
- Distal 18q deletion syndrome — MedlinePlus Genetics
- Proximal 18q deletion syndrome — MedlinePlus Genetics
Source: MedlinePlus Genetics, U.S. National Library of Medicine.
