People have two copies of most genes, one copy inherited from each parent. In some cases, however, the number of copies varies—meaning that a person can be born with one, three, or more copies of particular genes. Less commonly, one or more genes may be entirely missing. This type of genetic difference is known as copy number variation (CNV).
Copy number variation results from insertions, deletions, and duplications of large segments of DNA. These segments are big enough to include whole genes. Variation in gene copy number can influence the activity of genes and ultimately affect many body functions.
Researchers were surprised to learn that copy number variation accounts for a significant amount of genetic difference between people. More than 10 percent of human DNA appears to contain these differences in gene copy number. While much of this variation does not affect health or development, some differences likely influence a person’s risk of disease and response to certain drugs. Future research will focus on the consequences of copy number variation in different parts of the genome and study the contribution of these variations to many types of disease.
Topics in the Mutations and Health chapter
- What is a gene mutation and how do mutations occur?
- How can gene mutations affect health and development?
- Do all gene mutations affect health and development?
- What kinds of gene mutations are possible?
- Can a change in the number of genes affect health and development?
- Can changes in the number of chromosomes affect health and development?
- Can changes in the structure of chromosomes affect health and development?
- Can changes in noncoding DNA affect health and development?
- Can changes in mitochondrial DNA affect health and development?
- What are complex or multifactorial disorders?
- What does it mean to have a genetic predisposition to a disease?
- How are gene mutations involved in evolution?
- What information about a genetic condition can statistics provide?
- How are genetic conditions and genes named?

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