To understand OI, it's important to know how genes influence a person's biological makeup. Genes are chemical units of hereditary material that direct the development and function of every cell in the body. Genes determine which features or traits children will inherit from their parents. Genes affect growth, development, and appearance. They also influence one's tendency to get sick or resist disease.
Chromosomes are threadlike parts of cells that carry the genes.
Reproductive cells each contain 23 unpaired chromosomes. At conception, each parent provides a reproductive cell with one set of chromosomes. The two reproductive cells combine to form a single cell with a full set of chromosomes and corresponding genes. Most of the body's 50,000 or so genes function normally. Sometimes, however, a gene becomes changed from its original form.